I do like this but I'm slightly "concerned" (for lack of a better word) with using proficiency to increase AC. It doesn't have any precedent anywhere else in the rules. Proficiency applies to saving throws but I don't believe it is used to add to AC anywhere (correct me if I'm wrong).
No, no one else uses it as far as I know. We went this route months ago, however, and to our table is just "makes sense". Your defense, as a monk, with
unarmored defense is about your martial arts as we see it. Your
training is what allows you to avoid hits, lessen blows, etc. as well as a bit of learning how to take a hit. Since proficiency increases with level, your ability to defend yourself should increase as well. Since we go with either DEX or WIS, if the player also bumps one of these they bump AC. Think of it this way: in the long run, your AC will max out at 21 assuming you have a +5 for DEX or WIS. In the current game, you need a +5 in
BOTH just to get AC 20.
Monks are supposed to be battlers--not casters. A minor bump to AC won't hurt, and it lessens the MAD, which IMO is a good thing.
I'm hesitant to use Wisdom to replace Str or Dex for attack and damage. Other melee classes don't get that benefit. Hexblade is a special case and one of the few (if only) places to completely replace Str or Dex with another stat for both attack and damage rolls.
Yeah, this is one I am iffy on, myself, and I think changing it so you can use WIS for the attack roll, but not damage, is a good middle ground. It removes STR/DEX from attacking but those are still needed for damage.
Another route (since monk martial arts damage is so pathetic) is to allow monks to add their WIS modifier to damage on one hit per turn? Or maybe use WIS modifier as a bonus on one attack per turn? I feel like there is some way to work this in and I like it for the "vital strikes" aspect of monks.
shrug
FWIW, we did two other things for monks in our games:
1. martial art damage is bumped up one stage. So, d4 becomes d6, and in the end d10 becomes d12. It helps keep them on pace with other battlers for DPR.
2. part of unarmored movement for monks allows them to use their reaction to "instant stand" whenever they suffer the prone condition (knocked prone, tripped, falling, etc.).
Those two plus the revised Unarmored Defensive I listed above are currently our three monk "boosts". We like it and find the monk more competitive in terms of AC, damage, etc. to the other battlers now.
