>>15004822
>where every encounter is a monster closet?
Except it's not? The games generally follow a pattern of alternating between enclosed areas and wide-open arenas. Just going by that, you can predict that you'll probably want a shotgun or tommy gun, while avoiding explosive weapons, for the enclosed areas, while bringing out the minigun and rocket launcher for the more open sections. There's also looking at the pickups around the level and where they're placed. If there's a lot of a certain kind of ammo around, the developers are probably hinting that you're about to hit an encounter where the weapon that uses that ammo will be very useful. Many arenas have enemies charging you from far away, giving you time to read what's coming and appropriately prepare.
Instant weapon switching is appropriate for some action games. Combo-heavy ones, like DMC, benefit greatly from it. Most shooters aren't combo-heavy, though. There's no benefit to shooting an enemy with a shotgun, then quickly switching to a machine gun to take out the rest of its health. With shooters, it can be better to reward tactical play and forethought over snappy reaction-times and quick thinking. It depends on the game.