I said their name was stupid, not them as a whole, though I'm not fond of them, and do find them a bit silly (I know, I know, lots of D&D is silly, but Fiends aren't supposed to be, IMO. Fiends are supposed to be scary, not wacky). I certainly don't mean to offend anyone that does like them, I'm just stating my opinion as someone fairly new to the hobby.
"Devils" and "Demons" both roll off the tongue, as does "Fiend", but Yugoloth doesn't. "Yoo-goh-loth" doesn't sound like a 3rd main category of fiends, it sound's like you're cheering for someone with a peculiar name at a sports event "You go, Loth!" or saying that someone is reluctantly leaving.
I have no problem with it, either, I just think that Yugoloths are not good at doing that thing and were just made for grid-filling. There could have easily been another class/category of Neutral Evil fiends, and I don't think Yugoloths are good at fulfilling the idea of one.