The PHB allows spears and quarterstaffs to be used as monk weapons, yes. However, this allows them to be used in lieu of the Unarmed Attacks that Martial Arts usually allows. The bonus action allowed by Martial Arts and Flurry of Blows in the PHB specifies Unarmed Attack. Allowing weapon attacks instead changes this a little by adding the possibility of benefiting from magic weapons bonuses, so I feel like there needs to be a little bit of a trade-off. This is in addition to granting reach to a spear and a quarterstaff.
From a balance standpoint, that's where the Concentration check comes in. Most melee related concentration spells have pretty decent benefits, so the ability to add magic effects from weapons on your bonus actions and reach to a weapon that doesn't normally have it seems less strong but reasonable. Also, if you're concentrating on this, then you can't pull as many shenanigans by finding a way to load yourself with a concentration spell. I like that give-and -take, so I'd like to keep the stance with the concentration requirement.
Fair enough. Maybe, rather than moving the battlefield control to 6th level, the part about the counterattack or redirecting the original strike can be moved? Especially with the other suggestions about the disadvantage being strictly overpowered. This would cut down on doubling that, cut down on the wall of text for level 3, and give me a viable alternative for the higher levels. Thoughts on that?
I can get behind all of that. This also addresses Amnoriath's main critique of the feature.
The problem is that Amnoriath also makes some salient points concerning Open Hand's other abilities being lackluster. Deflecting Strike is quite so powerful, even with the changes. In response, I was thinking maybe expanding the monk's existing Stunning Strike. How about this change:
Disabling Strike
At 17th level, you have learned to use your Ki to keep an enemy reeling. If you hit an enemy that is currently stunned from your Stunning Strike with a spear or a quarterstaff, you can spend your reaction and 1 Ki point to extend the duration of the Stunning Strike for an extra round. This can be done up to three times.
This is a big change from the original, but I think it has some merit. It uses the same action as Deflecting Strike, meaning that you're essentially focusing on the one target and forgoing your defensive bonuses. Also, if you're using your reaction for anything else, this isn't an option. It does the same thing as just hitting it with another Stunning Strike but removes the saving throw. Also, it means you're not stranding an enemy and mopping up all of its buddies, since it requires you to hit the enemy again (meaning that in most cases that you've at least spent a bonus action on it in addition to the reaction). It sticks with the 3 Ki template put forth by the Open Hand ability but brings the power down and spreads it out over three rounds. Sure you and your party gain all of the advantages of having a Stunned enemy for several rounds, but that means that there's a distinct possibility of it coming out of the exchange alive, especially if another enemy starts harrying you and forces you to abandon this tactic. It remains within my intended "very strong against a single opponent, not nearly as stout against multiple enemies" intention. Thoughts?
My pleasure. I wouldn't mind that at all. If it can enhance someone else's game then I feel like I've accomplished something more than simply empowering my own game. Glad I could help.