I wouldn't say any real time dungeon crawler would qualify as a clunky FPS.
I'd say it's more like there are certain expectations of the gameplay based on weapons you can get. When you have ranged weapons that hit at effectively instant time at least my expectation is that the danger of instantly getting hit is compensated by having sufficient cover in the level design or strong movement mechanics to provide ways to counter the ability to get hit. Which is basically just things that encourage a faster pace of gameplay. It's just an association of that stuff with the flexibility of a different genre. I can't really buy getting like a railgun but like a greatbow would be okay (both are high damage but one uses a projectile, and at least to me it would be okay even if the projectile was very fast.), but on the other hand a hunting rifle makes sense to me but not a chaingun (high damage in one shot compared to higher damage over time).
I'm sure the difference in practical terms doesn't "mean" anything, but it feels different you know? I don't really know of any dungeon crawlers with automatic ranged weapons, usually they're either projectiles or semi-automatic.
Not sure if that makes any sense but that's how I see it.