Quote Originally Posted by Kane0 View Post
If you take the first to points (+1 to hit, +1 average damage) that's effectively the same as +2 to your attack stat which is what an ASI gives you, so this goes over the supposed balance point.
No it's not. The benefit is lesser because it only applies to one weapon, a weapon that is suboptimal to all classes except monk, and that for a monk can only be used on about half of his attacks, the other half being unarmed strikes. The offensive bonus is also only about half the benefit of raising your Dexterity, the other half being saving throws, skills and AC.

That being said, I really don't like Mearl's weapon specialisation feats. They utilise pesky +1 bonuses and weird action economy tricks (a reaction on your turn, wtf?). Kane's version is more user-friendly, but it's not very worthwhile for a monk. Your bonus action is immensely valuable, so you're always giving up offence or mobility when you use the defensive bonus. And guess what: getting +2 Dex or Wis would grant that +1 AC automatically.

It should be noted that if all you want is to keep using your quarterstaff at level 17, there is no need for a feat. The Martial Arts feature reads:
You can roll a d4 in place of the normal damage of your unarmed strike or monk weapon.
So a 17th level monk will deal 1d10 damage with a quarterstaff.

If you still want a quarterstaff feat just for the sake of it, I would suggest you make it a half feat that mainly gives you the reach benefit, the one part of this that is truly useful to a monk and can't be gotten otherwise. Monks need their stat bonuses more than any other class, so don't give them up for something that isn't worth it.