I watched plenty of '70s Hanna-Barbera animation growing up, so just because H-B did something, I don't consider that to be evidence that it was a good idea artistically.
You were not arguing the artistic value with:
Characters in animation need to be easily distinguishable on sight. Putting them in spacesuits would've made it harder to tell who was who in a long shot. The force field belts let viewers see the characters just as clearly as they could normally
That was an argument of being practical for the sake of character recognition
. The point was that character recognition (your point) was possible and proven in a series which mirrored ST to some degree. The TOS spacesuits could have been used for continuity's sake, and not sacrifice the audience's ability to recognize characters no matter their placement in a scene, just as it was accomplished on Sealab: 2020