I'm not sure why this thread is so absurdly obsessed about grappling being realistic when nobody seems to question whatever BS the casters are up to with the same demands of realism. Heck the monk can run on walls.
Spellcasting and realism. Hmmm... I wonder if that is a valid comparison to martial arts and realism. I can see wanting there to be a balance of the perception of effectiveness between the two.
There are those who have "real" experience with a diverse variety of martial arts, and the monk does not always deliver on the fantasy of a badass martial artist. That real life experience is far more easily quantified than real spellcasting (to be clear, I'm not interested in talking about "real" spellcasting). Martial arts afficionados may want their fantasy martial arts to measure up to at least to what they perceive as real capabilities, even before adding the mystical aspect on top of that.
I think the new Unarmed Strike rules (1+Str mod Damage, plus Grapple, and Shove options with Save DCs) is perfectly acceptable to represent basic unarmed combat. It doesn't need a complicated unarmed combat system at that level. That basic proficiency with nonmagical unarmed combat is not something that should rival weapons combat, especially when in D&D you'll be fighting monsters larger than you, with claws, teeth, and energy attacks. Go ahead and grapple even a mundane mountain lion and see what happens. But the mystic martial artist that is the Monk should be as effective as a normal weapon user and be able to contribute to a fight with a dragon.
How should a monk contribute to a dragon fight in a fantasy game like D&D? Not with something that looks like basic unarmed strikes. That isn't fantastic or fun. The Monk, the very pinnacle of an unarmed combatant, is the one class that deserves maneuvers and cool abilities that can embody a fantasy martial artist who can contribute to a fight with monsters. Martial arts afficionados have all kinds of styles in our mundane world. What can a fantasy game like D&D bring to the table that helps embody the martial artist fantasy?
The base level of competency people are looking for in their fantasy unarmed combatant are a variety of extraordinary mundane styles, stances, and maneuvers that can be reskinned as effective versions of mundane martial arts. Add some awesome magical options on top for flavor. It's fine if subclasses add some of those options. Let fantasy monks be tough movie-level boxers/martial artists, Batman-level beatdowners, as well as wuxia masters, ninjas, and element benders.
I do think monks deserve d10 hit points. Just about every mighty martial artist is portrayed as tough as nails that keeps getting up. I mean, Second Wind or something similar would really work for Monks too.