Given how prevalent the opinion is that Mobility is a feat tax for monks, I would guess more people feel like monk should be dipping in-and-out of melee. This is my solution to the same problem Treantmonk and Kane0 see with the monk's action economy: if you want to benefit from the monk's mobility you need to lose out on damage output (which I think lower than something like a TWF rogue).
Actually, this one is an artifact from when I had a different capstone. I can probably remove it here.
I agree with Treantmonk that one of the monks supposed strengths (its high defenses) doesn't really see play at most tables. Sure, they have Evasion before Tier 3, but so does the rogue. I shuffle it around so that an average monk player might be able to benefit from it before the campaign ends.
My tweaks are primarily focused around the PHB. If a player ever came to me with a kensei, I'd rework the sublcass as well.
That is an adaptation of one of the optional class features from Tasha's Cauldron of Everything. It is also worth noting that most subclasses for monk give ki features that use an action.