Yeah, demons and daemons sound way too similar and are basically the same concept (yes, so were a lot of folklore creatures that D&D draws from, but none of them had names as similar as "Demons" and "Demons with an extra A"). That would be like having two BBEGs, one named Ronin and another named Ronan.
5e doesn't use those first two, and I've only ever played 5e. Demons and Devils got back their normal names, Yugoloths got stuck with the phlegm-hawking of a name (likely because others pointed out that Demon and Daemon were too similar).
Githyanki is kinda weird, but it has an excuse for being weird (it was stolen from another book). Modron is weird, but at least it sounds like "drone", which fits the robot-theme that they have. I've also discussed my contempt for Slaad earlier in this thread. Aasimar is a strange name, as is Tiefling, but they're better than Yugoloth, IMHO.
Don't get me wrong, I don't hate all of the creature concepts for Yugoloths, I just think that they're irrelevant. Yagnoloths and Arcanaloths scream "Devil" to me. Canoloth screams "Carceri" to me. Mezzoloths, Nycaloths, Dhergoloths, Oinoloths, and Hydroloths just seem like Demons to me. (TBH, I have no idea what I would do with Ultroloths. They look like Aberrations, not Fiends, and have a similar flavor to Devils.) I'd just make Merrenoloths be their own Charon-selves unconnected to any category of fiends, like how Night Hags, Howlers, and Hell Hounds aren't Demons or Devils, they're just their own thing. I also think that it's perfectly fine giving different behaviors and personalities to different types of demons, so although a Glabrezu might just attack you on sight, a greedy Demon like a Nycaloth or Mezzoloth might be more willing to make a deal for truce or even mercenary work (until they can stab you in the back for a better offer, that is).