Wither skeletons spawning in roses shouldn't work on hard difficulty

Back in 20w21a, wither skeletons were made the only mob that could spawn in wither roses. On one hand, this is "consistent" with the behavior of other blocks that damage mobs, such as magma blocks. On the other hand, this change makes designing and creating a wither skeleton farm ridiculously easy. A lot of the technical community doesn't like this change because it removes the difficulty of creating such a valuable farm.

As a result, I'd suggest a compromise. On easy and normal difficulty, wither skeletons would be allowed to spawn in roses, but on hard difficulty, this behavior wouldn't work. This would mean that creating conventional fortress farms still has a use for people, but people who don't want to put in the work for it can still make a farm using roses on a lower difficulty.