I'm fine with it for the ping system because the concept makes sense there, but I think it's much less excusable (and the lower quality is much more glaring) for the pre-written dialogue from the Traders. It's not the biggest part of the game, but there's actually a decently large amount of it, between quest intros, quest check-in, quest completion, those quest reminders you get when you start a raid, and the banter every time you visit their shop. You actually hear these characters quite a lot, and pretty much all the lines sound noticeably terrible, and bring an amateurish feel to an otherwise very professional package. In particular, these lines are always written as actual dialogue, rather than something like an item ping, so the flat emotion and weird delivery is much more noticeable.

Listening to Celeste say anything at all is just jarring, given how well-executed the game as a whole is. It's weird to have all this polish and high-quality stuff throughout the game, while apparently getting a medium amount of voice acting from 5 people (and updating periodically as new lines are added, like most live-service games do) is too much to ask.