This is one of the things that makes it feel so D&D to me. The dialogue sounds like a bunch of players talking in-character, with all the odd mix of modernisms and traditional fantasy-world dialogue that entails.
And I love that, in the right fantasy property. No complaints from me about the
Legend of Vox Machina, and I'll probably be fine with the upcoming D&D movie if it has a comparable tonal vibe because, as you say it feels very much like what a D&D table sounds like.
The trouble is that this is a sequel and revival to a movie that was basically a lighter, kid-friendlier remix of Lord of the Rings, and inherited from that both a veneer of silted, "ye olde grand fantasy epic" tone and a world that lacked the population size and cosmopolitan elements which might make different characters having wildly different speech patterns, some more modern than others, make sense.
At the end of the day my issue with the dialogue is not it being intrinsically bad, but rather that it often lands awkwardly in ways that pull me out of enjoying the show and shift me over to critiquing the show. A show that, on the basis of high nostalgia, high production values, a serviceable story, a likeable enough cast, and a lead reprising his iconic role, would otherwise keep me in constant enjoyment mode.
