Problem with guaranteed damage from surfaces is it wrecks concentration for casters.
Every time I move through fire or someone misses me with a fire bomb I have to make a concentration check to keep my spell up. This can lead to 5 concentration checks from my enemies turn through the end of mine with no chance of saving throws or roll to hit me. Just 5 checks DC10 Con save or my spell goes byebye. Guaranteed damage should be limited to things like magic missile or specific powerful effects that still deal half damage on a failed save. NOT from the environment.
