The game dynamically scales ammo pickups and very rarely lets you run dry. I'd bet any amount of money that the vast majority of kills that have occurred in RE4 playthroughs come from bullets and not a suplex or roundhouse.
Sure, but that just means most people are terrible at the game, which is the norm for most games
The ammo also never really "scales up", simply because enemies becomes tougher (instead of 5 it now needs 10 bullets), so relatively speaking the amount of ammo remains constant.
Different guns let you approach encounters different (that's where the range comes in).
Still standing still, aiming and shooting. And all of it still triggers stagger animations, that's just free massive damage left on the table because you prefer shooting.
Enemies stagger and get knocked back in the later games.
....well yes, nobody said they don't, the difference is in the mood, RE7 enemies feel more imposing and dangerous because it takes more to even get them to stagger, that is the entire point of the feedback feeling weaker; if the feedback felt powerful, there would be a disconnect between what you feel is supposed to happen, and the actual result. Again, deliberate design.