Went in the crypt. Failed perception. Set off Grease. Being prone saved my character, but then crouching to try avoiding the fire trap doesn't avoid it. That's really not intuitive, and it makes for painfully slow progress through the area. It's a lot of design and kinda faithful mechanic implementation that will just be save scummed.

If you are talking about the room which shoots fireballs, I have solved that room with absolutely no rolls needed. There are multiple ways to solve issues in the game.

Did you try conjure water on the burning area? Puts out fires.
Did you try dash through the fire. Only 1 round of fire damage taken that way.
Did you try disarming the traps, there are many so the odds of failing ALL disarms and perceptions is pretty low.

You can also just put the urns on the vents like the tutorial tells you. I guess it's possible to fail all the perception checks and not see any of the vents, but very unlikely. Once you know the location of a couple of the vents, it's pretty trivial to figure out where the rest should be, and there's a ton of leeway for covering the vents.

And if you mess all that up, then yeah, you can just dash through it. I don't really understand what's painfully slow about it.

In addition, you can turn on turn-based mode and move your character when fireballs aren't going.

I can see why crouching doesn't work, if the fireballs are going for center-mass, it's unlikely that you're not crouching low enough and that it isn't possible.

Ohhhh, there COULD be an option to drop prone and crawl, though, that sounds like another thing which could be done.

It's again, pretty much as it is intended in 5e. The option to go turn by turn is always there, for both the players and the DM... this includes situations with traps and other environmental hazards.