Now I'm talking if you went Pure Sacred Fist. I'm sure if you took two level of flux capacitator and cross referenced with with the ossification of the sideways wombolatron you might get something out of it. And on Paper it looks really good. High AC, saves, etc. But in practice, they get ripped to shreds like a wet paper sack
1) Lack out of combat Ki regeneration - Monks at 2nd level gain meditation feat. The ninja spy regenerates while in stealth. Sacred fist only regenerate when punching monster face. And it looks like the only way to imrpove their monster face punching ki generation is by popping Turn undeads in combat, which if fighting undead makes it so you get no ki generation if you're really good at turning undead. The lack of non-face punchy out of combat ki regeneration means that some of the ki power abilities like Ki Bolt are pretty much useless. Even fi you're in combat, your Ki pool will be drained faster than a moshpit at a Celine DeLeon concert giving you a single attack per combat and nothing outside of combat.
2) Lack of ranged weapon options. Not really that important of a thing except for all the monsters that cannot be face punched. The traps and doors that have to be hit with a ranged weapon. Etc. If you equip any ranged weapon, you become uncentered (So now all your abilities go poof) Monks can at least equip Shuriken proficiently, Sacred Fist should be able to so they can keep up with the jones and participate in some ranged combat when they cannot face punchy things rather than having to use the shuriken non-profiently or go uncentered with throwing knife/dart.
3) Its skills and starting equipment for veteran still pretend that its a standard heavy armor shield using paladin. The starting equipment can be adjusted, but Tumble not being a class skill kinda hurts. And I'm not sure, but I got this feeling that the chests are rigged towards standard paladin, cause the amount of fullplate armors and heavy shields I get are staggering.
4) Enhancements honestly kinda suck. Sure there is some jewels, but like the capstone level 20 one? a small boost to a few numbers, and then 25% fire absorption? The sacred fist get a lot of saves.. Heck this capstone gives you 6 to saving throws. You get a bunch of them in earlier abilities. And you have evasion. You've got typically a 5% chance to take fire damage. Maybe i just don't know absorption mechanics that well, but it doesn't seem to be really that ground breaking when you compare it to something like sacred defender, who gains a bunch of defense boosts and the ability to keep fighting even if they get killed. They also get the abiltiy to stop (Though far late game) magic missiles. Which turns out to be the big killer IMO. The Sacred Fist just gets nickeled and dimed to death whenever there is a spell caster cause they spam the heck out of those MM.
There is a few of these "If you fail" enhancements in SF. The improved evasion one that if you roll a nat 1, you take less damage (80% less), the one if you are helpless you take 15% less, and the capstone.