The difference between Saudi and Qatar world cups will be seen when it actually happens and we can only make assumptions so far. But the biggest difference was that Qatar just didn't had any stadiums or anything, and had to change the whole timing of it, we literally saw world cup in November because of them, makes no sense at all, and it was a stupid decision, hell it was proven to be corrupt and just fired everyone involved, but because of legal reasons (since Qatar already spent a lot) they couldn't take it back, so it was known it was bribery and yet they still had to go with it.

Saudi could be different, in the sense that they at least already have stadiums and infrastructure in place, they could make some improvements, but they are not going to spend billions to actually build it. I feel like it is still not as good as lets say England or whatever, but it is definitely good and I believe it should be better. Not guaranteed though, we still have to wait and see.