Is this meant to be a joke? I know people have this obsession with Sancho, but he is not better than Martial . I think people will be in for a shock when Sancho plays in the premier league. He wont produce the Dortmund numbers here because teams don't give you that freedom here. Defending in Bundesliga is a joke.
Counter argument: Danny Ings has 20 goals this season so far.
Besides that the last player of that category who went to the PL (De Bruyne) has had no problems to keep his BL numbers.
It's anyways weird to argue that BL defending is a joke considering some of the recent goals ManUtd has scored with a lot of help from the opponents. Defending is of very mixed quality in all top leagues or do you honestly think there is a big difference between the mid and lower table teams in England, Spain, Germany, Italy or France?
The real difference is usually between the top teams but then one should acknowledge that this is certainly not an area where EPL top teams currently shine outside of Liverpool. Chelsea, Arsenal and Tottenham for example struggle defensively this season and City also has been weaker than usual.
It is of course always possible that a player will struggle at a new club and not deliver the same kind of numbers but it won't be because of better defending or did someone like Sanchez fail at United because everyone in the EPL started to defend better once he arrived at your club?
The most likely reason for Sancho not producing the same numbers is the simple fact that United is less attacking than Dortmund (at least so far).
In regards to comparisons between Martial and Sancho:
Keep in mind that Martial is now 24 years old and delivers these numbers for the first time after some disappointing seasons and as striker.
Sancho is just 20 years old and is now 2 for 2 in exceptional seasons and that while not being on a particular hot streak (you can feel/see that there is still a lot of room left in him).
Even someone like CR7 needed three seasons before he started to produce such numbers in his 4th PL season.
So I don't care too much about stuff like "who is better" because judging players at different stages in their career is always difficult but so far Sancho's trajectory is definitely on a different level than Martial's. Doesn't need to stay that way but there is a reason why Sancho's numbers are EXTREMELY rare for such a young player.