I actually think the monk isn't nearly in as good of a shape as you suggest, with all due respect.I don't think it was a big mistake. The monk is not that far from being decent. The new subclasses except for the open hand are decent. The idea to remove ki point costs is decent. It should not be that hard to remove them. Then add some damage feature at level 11 and we are looking at a useable class. And from level 14 on, it definitely has its niche as a very hard to disable class (all saving throw proficiencies with (possibly double) advantage for one ki point if needed).
Monk, despite having simple weapons, is heavily biased towards making every attack unarmed, considering all the benefits later levels give to unarmed. It makes it hard to play out archetypes like being a Jedi or any other wannabe wandering samurai archetype, which are definitely part of the monk class fantasy.
Compared to the Fighter, the damage from a Monk is decent. Not unbalanced. HOWEVER. With the addition of Weapon Masteries, we are grossly missing utility that every other martial gets. Even if you use a club or staff for one attack, that leaves one or two attacks that don't benefit from a Mastery. The removal of growing die bonuses from weapons is also kind of a rob - that's the Monk's equivalent to Rage bonus damage.
Compared to the new ... every other martial, monks are grossly missing utility. Rogues and Rangers are great at utility by default. Barbarian's new Primal Knowledge make them excellent scouts and pretty good at threatening people to get their way. Fighter's new Tactical abilities are great. Paladin spells and abilities have always been good. The closest thing to utility Monk has is... jumping and Acrobatic Movement at level 9. Nothing really that good.
Compard to the Rogue's Cunning Action and Uncanny Dodge (for FREE), the Monk's Patient Defense and Step of the Wind are lackluster. Compared to Cunning Strike, Stunning Blow is a one trick pony. And the monk's stuff takes a resource and potentially damage (everything's bonus actions), while the Rogue can spam their stuff every turn at a minor 1d6 cost. There's a lot to unpack with the Rogue comparison. Weaker abilities, weaker survivability, questionable role in party...
The de-Asian-ifying of the Monk was a huge failure, so they need to actually work that out too.
The power curve on the monk relies on not just more ki, but also getting better damage and more attacks at the level 11 and 17 bump. This has been passed off to the subclasses, which ... sometimes do things like just give you more mobility. More mobility is good, but it doesn't help the monk's damage at higher levels, which is lacking.
Lack of feats that monks can use - instead, they're dependent on going all in on ASI bumps. Which is not a good design point to be atl. The point of feats is to allow customization of characters. Monks are simultaneously HEAVILY resistant to being customized, more than any other class, and have been cut off from options that would allow customization if they could afford it. We should have more ooptions and flexibility, not less.
These are all things that need to be addressed, and quite a few of them aren't simple.