The monk can spend a short resource he has X of to accomplish Y effect but the fighters encounter resource he has Z of ..... if i allow someone to use Skill Q to accomplish something similar to one of those who is getting the short end of the stick? how difficult really should it be? is it going to be too erratic to be even worth trying? (when should it not be)
I mentioned before that someone gave an epic difficulty answer on something and someone else assumed my characters reaction was going to be much earlier in the sequence and didnt have to even do the full follow through. (to help an ally out of falling like someone might do with the feather fall spell the other one assumed you could get the grab in before the fall and the other thought jumping down with a falling friend to cushion there fall was humongous).
One table its a nearly impossible and the other its moderate thing. Because of really slight assumption differences. That I just do not see hashing out in a session zero. I just do not see it. I see first edition my character is drowning over swimming rolls eraticness because the dm was forced to improvise all over again.
I don't disagree with any of this. Session zero sets an expected level of capability, and there can easily be variance between tables. That's because the DM is empowered to set those levels. That was intentional.
I find it's more work to adjust healing or magic levels than it is ability checks. Players might need to explore what the characters can do more in this edition but that was the trade-off. Consistency vs DM empowerment can oppose each other.
Fortunately, campaign books tend to have DC's already applied.