No, I wasn't heavy at all for my slowest 10K. I might have been even lighter than when I was at my fastest. I was just my first, and it took 58:xx, running legitimately as hard as I could - you could see my agony and effort in the little race photo proof that I still have somewhere. Later on I was able to do 29:28 for 6 miles in training, and I think I was in sub-30 10,000 shape at that time, but I never raced a 10,000 on the track. I didn't race at that time except for on-campus stuff (intramural XC, that I won 2 years, over redshirt D1 guys) because I didn't have a car, was shy, and didn't know how to get into legit races (this was the 80s, before internet). I had health issues with chronic fatigue or overtraining after college and was never the same again. But I did manage to record PRs of 25:0x for 5 miles and 32:06 for 10K on regular running, but no workouts or serious training.
No, I don't need to think smaller margins of improvement for guys running since their school days. Life and training is or can be much, much more chaotic than you make it out to be. I have see huge disparities in level of performance in myself, and the guys that I have raced for nearly 2 decades. What about wejo? He trained hard and raced hard for 4 years in college and ran only about 30 for 10,000, and then suddenly was running close to 28 flat? While also training in Flagstaff (clue your drugs angle...). Sometimes people figure out their training and make big jumps. Sometimes people are half-assing their training, like Jim in 2014. Sometimes, some years you just don't have it, or you don't bring it, or you aren't serious about training for many reasons, have other priorities, or your real job sucks and impacts your ability to train, none of the reasons needing to be excuses. In my personal experience, life and running is chaotic, not linear. When I brought up Geb, you make an excuse for him. Why didn't you do the same for Jim?
Even if you don't buy that Jim's thinking that he didn't come close to maxing out in college, you really think a 13:52 runner who runs a 1:08 half marathon actually trained seriously for the half marathon? An equivalent half marathon performance to that 5,000 is 5 minutes faster. He could have jogged a 1:08 in training at 3/4 effort when he was in 13:52 shape. I can't take you seriously when you write stuff like, paraphrasing, "Jim's only a 1:08 half marathoner," and then draw seriously distorted conclusions from that.
And I do buy that Jim's thinking that he didn't max out in college (he optimistically thinks that he could have run 13:20-25 if he focused on track after college). He'd be the one to know how maxed out he was, just like I know I certainly never came close to maxing out my PRs.
You are single minded about drugs and overly paranoid. The rest of us will consider Jim legit, barring someone opening up and saying something like, I was his supplier, or I injected him, or I was his housemate and found EPO in the fridge... and identifying themselves, like Armstrong's accusers. I don't think that's going to happen because I think he's legit.