I would agree that I think somethin' special was up at Sky.I guess we all have our assumptions (usually based on what we've learned about the sport).
I'm inclined to believe there was a very specific regimen at Sky with the right people behind the scenes in the team & also right people behind the scenes outside the team which gave Froome his advantage.
I don't think dope is enough. It takes an extra layer of advantage on top. I mean that's what Armstrong had (I'm talking about the UCI backing him with Verbruggen to the point where he was advantaged).
I think Froome's "game over" happened between his Salbutamol 2017 Vuelta positive & his Giro 2018 Landis-esque 80km solo raid. I also think Ineos had already decided he was done after that.
That's just my own guess.
I would add - injuries and age also add up. And dope, no matter how much, does not solve all the problems.