As is sometimes the case, the truth lies somewhere in-between.
A lot of sprinting is about native talent, and about not effing up that talent.
Great sprinters are born and not made, but the very best sprinters are born and then made.
Take a look at the 100m results of the African champs this year:
http://en.wikipedia.org/wiki/2012_African_Championships_in_Athletics_%E2%80%93_Men%27s_100_metres
Those are the times you get with talent plus a bit, but not the best, of training. The final ranged from 10.29 to 10.58 (-0.9)
Make no mistake, some of those guys have what they consider to be semi-decent training programs. You can clearly see that absolutely none of those times are "world-class" by how we normally judge.
Take a look now at the 100m results of the 2012 NCAA champs:
Those are the times you get with talent plus some decent training. The spread in the final was almost identical to the Africans, ranging from 10.28 to 10.45, but into a slightly greater -2.3 headwind.
Both Africa and the NCAA ranks are loaded with talent, I would argue at the exact same level, in the aggregate. The only difference is better training in the NCAA's.
The best NCAA guys go just-sub-10, to around just over 10-flat, with some wind.
The best-ever NCAA guys go high 9.8x
The best-ever clean guys go mid-low 9.8x
I've said it a million times, and I'll say it again: everybody who has gone a real 9.80 or below (this removes guys like Mullings and Carter) is juiced, with the possible exceptions of Gay's 9.69 (+2.0), and maybe Gay's 9.71 in Beijing. I offer no ideas whatsoever about Powell at the moment, he is off the table.
Gay has the fastest-ever clean absolute 100m time because he got lucky with wind (or the wind reading was a scam). Bailey and Surin are the clean benchmarks, especially Bailey with his inferior start after false-starts in Atlanta '96. Although I'm not at all certain about Fredericks cleanliness, he is for me also a benchmark with his 9.86 into a headwind.
That's it, plain and simple. Johnson, Greene, Montgomery, Blake were/are all juiced. Gatlin and Bolt are irrelevant due to the possibility of lasting benefit from doping.
The only real question is Powell, who I really can't figure out...but that's OK, even he has problems figuring himself out!
In the 100m, the most important thing is to not get in the way of talent.
Look at Gemili--that guy's race is beautiful. THAT is raw talent, both physically, mentally, and formally. If well-coached, he will be at or near the top some day.
Look at Lemaitre--that guy's race is horrible. Has he improved due to coaching? Maybe, but you really can't tell.
Would having Francis as a coach improve either of these guys, assuming they didn't do drugs? Again, hard to tell. Different things are good for different athletes, there is no one-size-fits-all approach for sprinting. Some people are uniquely susceptible to certain injuries, but are NAILS otherwise.
For my money, the basic equipment--musculature and neurology--MUST be in place. Then, what a coach should do is to determine what variation of "ideal form" an individual athlete would benefit from the most, and shape the athlete's program to achieve that fastest possible form. Adding power through musculature and neurology are important as well, but they happen naturally, and are not that difficult to achieve. Power and neurology are often adequate, but used imperfectly.
The thing about resting neurology is important in the "not effing up" a sprinter's basic talent. A coach/training program can DESTROY a sprinter, as it can any athlete, if it unfavorably exacerbates weakness.
The problem with lots of coaches is that they don't listen, and that they work with constraints like time of day at the track/weight room (which is a problem not with the coach but with circumstances). Like somebody else has suggested, sprint training is high-level stuff: go hard, or go home, most of the time. There is almost no use to training anywhere significantly below your ability, which means that you have to be READY and PSYCHED to do a workout--otherwise you will get no benefit, or worse, slide backward through fatigue and injury.
I have seen lots of guys try the "don't go so hard" approach in workouts, thinking that their efforts would cumulate. They didn't. I can't tell you how many guys I believe could go 10.7 who I have seen stuck above 11.
The VERY fastest guys I have ever known, who have been some of the VERY fastest guys ever, would never go half-way in workouts: they would either give it their all, or slack off so completely that all they did was a sort of extended warm-up. There is no middle ground with short sprinting. (I don't include 400m in short sprinting.)
The only things that make a good coach are listening and observing well, knowing some of the basics of training, and knowing the personalities of individual athletes so that they can be made/encouraged to respond. I think there is a HUGE over-emphasis on the technicalities of "training", and not nearly enough on putting together training groups, selecting music, and creating the best possible environment.
Let me tell you, back then, there were some good environments, not just in Toronto, but also down at Santa Monica. Now there are probably some at some colleges, and also definitely down in Jamaica. Was Francis responsible for the good environment in T.O.? That is the question.