I never said that, given sufficient supply of the same caliber of athletes for each event, 16x200m wouldn't be the most efficient. My point was that it would be hard to find an example where ONLY using 200m runners (and 16 of them) is going to be easy to find where they are of the same caliber as, say, elite 400m runners that might be in the same program.
Let's start with high school. The average sized public high school in the United States has approximately 1,000 students (+/- ~150). So let's say there are ~500 boys and ~500 girls at the average sized public school. Now, average boys turnout for track is often around 10%, which means the average sized high school in the United States probably has about 50 boys and 50 girls. Of all the events in track, the 100m has about 12% of the total results and the 200m has about 10%. If you want to say that 100m guys are willing to step up to the 200m on this hypothetical relay and have similar performances to their 100m races, that means that about 22% of the team is going to be 200m types. Throw in the 400m guys (~9%), and you're talking about 30%, give or take. 30% of 50 is 15. So, not only does the "average" sized high school not have 16 different athletes that would consider competing in a 200m race, but even the JV and Frosh/Soph squad guys are going to be involved on this relay. Now, the question would become, would the slowest two kids be able to combine, each running 200m, for a faster time than the fastest 400m runner on the team? I don't know, I think that's asking a little too much. I mean, you're already a guy short! And, I don't know about you, but I've seen some 24.high/25.mid type JV runners and Frosh/Soph runners. Actually, I've seen a WHOLE lot of those types - they probably make up almost a quarter of the athletes that compete in the 100m/200m races. Don't you think that, on an average sized team, you aren't going to find an athlete that can run 50-51 for 400m? Because that would be an improvement.
Now, for colleges? Just how many athletes do you think get scholarships for track? And just how many walkons do you think there are? Take the University of Washington, for example (chose them because it was quick and easy to get their rosters for the past two years, and because they are bound to be above average for all of colleges given that they are Division 1 and that they are part of a premier conference). There were 57 athletes on their 2010 roster, including 10 sprinters. There were 52 athletes on their 2009 roster, including 9 sprinters. So, for an "above average" sized college, you have roster numbers comparable to the "average" sized high school. Yes, they'll get some decathletes or jumpers to help cover, but it is silly to propose that the optimal choice would be to bring in non-sprinters for a relay.
As for the professional level? Well, again, I don't know the exact numbers that Nike or Adidas or Reebock or Asics or anyone else signs under contract, but I'm not sure it would be all that much beyond a dozen elite sprinters? But yes, I would agree that it would still be optimal on the professional level to have 16 guys run 200 meters.
This would be compounded even further if you started considering 300m legs and the like, of course. Because at that point, I'm pretty sure I'd rather have my top dozen athletes or take on as much as they could before "losing steam" in most cases. Because that pair of 22.mid guys can probably run 34.mid for 300m, but could the #14/15/16 200m guys really average 23.low? Or that pair of 23.mid guys that can probably run 36.low for 300m vs. those #14/15/16 200m guys that probably couldn't average 24.low?
Again, it would be silly to think that the #15/16 guys on most teams would really be better than having other, FASTER, guys run slightly longer legs.
I'd expect the most optimal for most teams is probably something more similar to mostly 300m legs with maybe a 400m and maybe a couple 200m, depending on the team's strengths and depth. Really, you don't lose much speed extending from 200m to 300m -- maybe 2.5-3.0%. And when you're comparing the best on the team to essentially the worst (in that discipline), more often than not that difference will be quite a bit greater. 3% is roughly the difference between US Top-100 and US Top 1,000-1,250 in high school, for example... and it would be quite an accomplishment indeed if a program had their #15/16 guys as top 1,000-1,250 in the entire nation...