So...."bad chemistry = bad handoffs and DQs"; huh?
TL;DR ultimate point:
The US is so fast they should be able to "basic" exchange their way to victory, regardless of "drama" and "chemistry". There is no Bolt/Blake tandem for anyone the US faces now...the US essentially HAS that tandem now. If you've got the fastest people the way the US does right now, the chemistry excuse goes out the window. They could hate each other, complain about practice, and ponder about getting off the relay, but they should STILL be able to get the baton around and win going away.
Why would I say this? Lemme tell you a story of how chemistry doesn't mean 'ish...
I was on a lower division college 4x1 team that was LOADED with talent (especially for a low division), but had virtually NO chemistry. The second leg was a football player who came out for the outdoor track season because he had dreams of NFL grandeur and either believed or was convinced by others that showcasing and/or improving his speed would improve his drafting viability. He HAD run track in high school, though, so it probably wasn't an outlandish idea to him. It worked, he was actually pretty good (again, especially in our lower division). But....chemistry? I mean, he was actually a fairly cool, dude as far as I could tell, but he actually booted a guy off the 4x1 team from the previous year (he was a major upgrade on pure talent and speed alone) and interrupted whatever chemistry had already been built up from THAT group. A good example of the LACK of chemistry he brought to the table was that he kept switching the baton from his left hand to his right hand mid-run. This is an OBVIOUS and BASIC NO-NO. We told him as such. All of us, from the fastest guy on the team (faster than him, older than him, the would-be leader but he was a "beta" until the clock started) to the head coach. The second leg football player kept scoffing at us and kept saying he wasn't comfortable with the baton in his left hand. I believe he actually felt he couldn't run as fast with the baton in his left hand. Eventually, he acquiesced...and ceased switching hands, but I swear when I used to look at the tape that he would still fiddle with it in his hand, though I'm guessing he wasn't actually switching because the third and anchor leg were getting the baton in the correct hand and in the seemingly correct positions after he stopped switching.
The first leg, the best starter on the team, didn't even want to be on the relay. He and another sprinter (the guy who got booted off the 4x1 squad by the football player) were fed up with the coach (again, this was a low division college team) and had actually hired a personal coach and was writing up all their workouts for them. The head coach was presumably our "coach" and telling us what to do for workouts and such, but over the off season there was a big snafu and the first leg had worked out a deal with the head coach to be allowed to do the workouts HE wanted to do. Now, to be fair, the head coach was an idiot and, being the low division team we were, we didn't have our own true sprint coach. But...the first leg was inevitably secluded a bit from the rest of the team as a result of all this drama. He had his own training schedule, and point in fact we actually had to have a sit down on if and when to practice our hand-offs during the week because the first leg didn't think the hard sprinting of hand-off practice fit within his training schedule properly. Eventually he, also, acquiesced and did the hand-offs with when we had them scheduled. But he resented it.... The whole charade actually had the entire team divided as the head coach would gossip about the whole thing to his distance guys and everyone would whisper and side eye at each other over this-and-that. It never really calmed down until everyone just fessed up to the fact that the sprinters -coached by personal coaches or "coached" by the head coach- were capable of winning the most events and winning tends to shut everyone up.
Anyway.
The third leg just didn't understand hand-offs. This was a 21/22 year old man who had a concept of 4x1 hand-offs like a high school sophomore. He thought the longer he held onto the baton in the exchange zone, waiting for the anchor leg to get "closer to top speed", the better off it would be for the relay and our time results. He would literally try to sit on the anchor leg through the zone and wait until he sensed the time was right (meaning the anchor leg was starting to fly away from him) to give the audible cue for the baton exchange. Time this poorly, and you suddenly have your exchange partner running away from you before you can get the baton in his hand. So, of COURSE this led to a drop baton in the middle of the season (but at a dinky meet). The second leg to the third leg exchange also had a dropped baton in a meet, and at ANOTHER meet the first leg to the second leg had a botched (albeit still legal...barely) exchange. All in all, in the first five meets of the year (so, half the season) they dropped the baton twice and had various degrees of "botched" but legal passes in the other three runs.
Somewhere around that fifth meet, the first leg was threatening to ask off the relay. Additionally, an assistant coach was offering the anchor leg (the fastest guy on the team and in the country in their lower division) advice that maybe he, too, should ask off the team perhaps as a kind of power move to try and get the rest of the team to get their act together. Of the four guys on the team, the only one who even really wanted to be ON the relay was the third leg, who was the slowest of the three, unable to make much of a bang in the individual events, and perhaps only marginally better than the fifth option (the guy the footballer replaced on the second leg). And, remember, he also didn't understand true relay exchange mechanics, so he was part of the problem, too.
After that fifth meet, nothing really changed....but the baton starting getting around the track with more regularity and with less flare ups. On the face of that, you'd think chemistry improved...but really it's just that none of the four guys had enough of a tantrum to quit the relay, and even basic "safe" exchanges would virtually guarantee victory; we were good enough to beat a fair amount of DI teams if we ever faced them. Then, seemingly out of no where, we dropped almost .40 seconds from our time at our national meet, won going away, and were arguably close to breaking 40. At one point the relay that looked like it would self-implode and the coaches might have even been goading it to, ended up being the first national champion track result for the program in something like a decade.
No discernible change in chemistry was made, and again I swear I saw the second leg fiddling with the baton in his hand during his run at nationals when we ran our fastest. The third leg even forced the second leg to stretch HARD during their exchange in the final. The video isn't clear, but I think a case could be made that they got close to running out of the zone in that final. Maybe that's how we dropped .40ish, I dunno. He still sat a bit on the anchor, too, during their exchange...the guy who wanted the relay the most may have been the one at nationals to put it at most peril. But, it didn't matter, we won anyway.
Afterward, the parents of the relay team petitioned the school for championship rings to be given to the relay team, which had never been done before and was only done for the football team. The guys didn't really care (except maybe the third leg), but it was apparently a bit of a poop-show on the matter until the school acquiesced. It then forced the school to go through the archives and give rings to allllll the other relay champs (and maybe individuals, too?), all because of the parents bologna petition. The parents didn't even know the first leg wanted to quit the relay most of the year and the anchor was advised by the coach to step off the relay and focus on his individual events...
So. Chemistry my butt.
As an aside, the anchor leg ended up blowing his hammy out right after the relay win, and the first leg still gained All-American status in his race. One of the things the first leg was upset about with hand-off practice was injury risk in the flow of his personal training plan. The anchor went into nationals with something like over a tenth lead on the field over 100 meters, but he took dead last, walking the last 50 meters of the 100, due to the hammy blow out. Kind of ironic.