I think it's also pretty unlikely that this alternate-universe first TTRPG would attempt to be generic fantasy. Like AD&D, it would have an implied setting based on what tropes the authors wanted to simulate.
For example, we could have a more productive debate around the question "What if the first TTRPG ever published were trying to simulate a medieval fantasy setting inspired by Robin Hobb, GRR Martin, and Arthurian legends?"
Indeed, I think it's quite likely it would have more than implied setting. D&D not having a setting was really weird. The odds are pretty good it would have a setting.
The question is what that would be though.
The 5e monk class is reasonably close to the latter.
With respect, no, it absolutely is not. It's focused entirely, and quite tightly on the characteristics of a mythological Shaolin monk. The entire chassis is based on Shaolin myth specifically.
If we look at the Monk, we can see the follow doesn't fit martial artists in general:
1) It's exclusively DEX and WIS based. Absolutely inappropriate for a lot of martial artists.
2) Step of the Wind is a very specific thing to a certain kind of Kung Fu Shaolin type.
3) Unarmoured movement likewise - especially the 9th-level upgrade. There's a small minority of martial arts types this does fit (including Ninjas, ironically enough), but not the majority.
4) Slow fall - common enough it should optional, but nowhere near enough to be a mandatory feature.
5) Stunning Strike - Explained as a weird monk thing and whilst you can "re-fluff" it, it's a weird monk thing. It's also terrible because the entire class balances on it.
6) Stillness of Mind - Again perhaps optional, definitely not mandatory.
7) Purity of Body - Pure Shaolin.
8) Tongue of the Sun and Moon - Extreme Shaolin, like wildly wacky.
9) Diamond Soul - Deeply Shaolin though so powerful I think few would object lol.
10) Timeless Body - Shaolin.
11) Empty Body - Shaolin.
The majority of the subclasses, are either Shaolin-aligned or very "monastic martial artist" aligned, with only a couple really reflecting broader martial arts themes. Plus there's more minutiae on the abilities which makes them very deeply "monastic martial artist".
What's sad is, as A5E and other show, if you stripped about 60% of the abilities and refactored it to not be DEX/WIS based but also potentially STR and INT, CON or CHA based, and gave people a bunch of choices of ability, you could redesign it pretty easily as a generic martial artist. WotC I don't think can even process that idea, though, despite the fact that few people play Monks, and I can't even think of a single popular podcast character who is a Monk (correct me if I'm missing someone).