it apparently varies from stadium to stadium and also from section to section, although it's probably universal that the cheap seats are narrower and closer together and the more expensive premium seats are much wider and further apart.

Supposedly the seats vary from ~18"/19" - 26" wide. But a big difference is that unlike a flat auditorium, the rows are inclined, so the person in the row behind you is not breathing right up against the back of your head - they are elevated when sitting behind you and you are elevated sitting behind the row in front of you. That's pretty much the definition of a stadium and you get that configuration with bleachers that have multiple rows that go up at an angle.

Standing all on the same level means you are right around each other - which is probably why the churches were hosts to some big super-spreaders because outside of the huge "stadium seating" type mega churches, the average church pews are all on the same level, one row behind another. The same applies to rooms using rows of chairs all on the same level.