That was your point :
None of these apply on Martial in his first season, he was playing in a disjointed team who finished 5th, under a past it manager who was more interested in fighting with the press than managing the team, alongside awful teammates. So if he actually succeeded in this first season then it's up to him and him only being good enough (that's regardless of me actually thinking Martial's first season is overrated anyway).
Sancho, meanwhile, has been awful for us ever since he signed, except for the rare games here and there, so both aren't comparable. You're giving an example for one who started well and faded away later on, which isn't the case for Sancho, he has been disappointing since day one.
Anyway, the point about the league was just a response to him "being fantastic at BvB" which doesn't really mean much for how well he'll perform at United.
I get your argument, Martial came out of the gates firing, then had a lull, and finished the season decently, we know the rest of his story. I used him and Bruno as an example to show players coming from 'weaker' leagues, and showing no issues of adaptation to the league before they are fully imbedded into the team, because the league itself is not the reason for success or failures IMO, I don't think it even enters in the top 5 reasons why a player will succeed or fail.
Agreed about Sancho, he seemed fantastic not just in the Bundesliga but in the CL as well, but he simply never kicked on at United and City was fine with letting him go before all of that. He still has time to turn things around, but he's definitely been a dud from the get-go.
Players from Bundesliga have said verbatim that it's far more difficult for a wingers in the premier league. Believe what you want. Sancho has looked good in only one team and one system so far (national and club)
They can say that all they want, I'm saying that's just a lazy analysis/excuse without trying to dig in deeper and look at themselves and their circumstances IMHO. It's easier to blame the league for your failures than looking deeper into why you've failed.
Messi at PSG was poor last season, couldn't even crack double digit goals in Ligue 1, somehow was banging them in the CL, and it's clearly not the league, but Pochettino's tactics and the absolute mess it was compared to what Galtier is doing now. Again, there is no exact science why a player will succeed or fail in a different league, but the league itself is way down the list of reasons to me, too many examples to show why it's a flawed logic. Whether we're talking about Mikhi, Sancho, those players didn't come into a team that was clicking on all cylinders and stunk the place up, where that would maybe give more validity to the league point, they just fell into the same crappy team that many other players lost their ways in. Werner is another example, it's not like strikers at Chelsea have been amazing for the past decade, why is that? Is it the league even though Lukaku was banging them in with two previous English teams before? This isn't me saying the PL is not faster, or has more qualities, but it also has a lot of piss-poor teams like all the other leagues where a good player should be able to find success. But if you're in a team that's poor tactically, mentally, with low morale, poor chemistry, maybe the city sucks, all those things are far bigger factors to me than the actual league the team is playing in.