This is the biggest factor IMO.It's really really common on F1 for a seat to be bought like that, Mazepin has had a tough start but he has a better record in lower disciplines than some we have seen in the past.
The car was quicker than the Mercedes for the first couple of races, at worst it's a match now, the potential wing ban may change that in future races. Mercedes are doing a better job with strategy, although that's easier to do with Hamilton as he's so consistent and so fast. Perez not being as reliable a wingman as Bottas isn't helping them either.
It doesn't allow them to vary strategies, they just have to plan one and go for it.