I would say the general assumption here in the Clinic is that Sky was running a very sophisticated team doping program for all of those years (together with all the other marginal gains stuff, which probably helped marginally too). Probably connected with the official UK efforts for the London Olympics. This program hasn't really been revealed yet, and maybe never will.Nearly 1400 pages on this, so maybe this has been conclusively befoe.
In 2011 Chris Froome was outsider. He was earning 80k a year, not that much, few contacts in the sport. But then he apparently took something that catapulted him, according to the Clinic, from an autobus dweller into a contender overnight. Tour of Poland etc.
Now let's say it was all drugs, Froome has extended that form for at least 8 years. He is rich. There's been no actual doping problems
So the question is 'Why is he only one?'. Surely others would try their hand
Maybe not everything Sky was doing was technically illegal, but in some grey zone of legality. I personally don't think they were using blood bags or anything as crude as that. Why was Froome a part of that despite being an outsider (which he was) - why wouldn't he be if he's on the Vuelta team?
The second assumption is that not every athlete profits from doping equally. This is probably uncontroversial, various genetic factors makes people react differently to all sorts of drugs. Some people for instance are basically immune to morphine. Training level also matters; if you pump a fat male 18-year-old full of anabolic steroids and make him work out under professional guidance for half a year you'll see a more radical transformation than if you do it to an already fit 30-year-old. And if that 18-year-old actually has excellent genetics but just never did anything, then even more so.
It is possible that the factors Froome himself stated for his improved performance (recovery from illness, better coaching, more focused peaking, etc.) and the well known yellow-jersey syndrome (if a rider has a real goal in mind it's easier to give 100% than if you don't think you have a chance anyway) in connection with whatever sinister program Sky was running produced the result we know.
It can be both imo. He probably did try harder, he did train better, and maybe he also did some things along the way that weren't within the rules of the sport.