From the BG3 video posted above:
"The shadowlands...makes back home in the underdark seem quaint"
"I won't have to worry about the sun, at least"
"Even in the Underdark, I never saw gloom like this. It's unsettling."
"Alas, it's the only path to Moonrise Towers. We have to push into the dark."
"So, the Nightsong is key to Ketheric's invulnerability"
"Nightsong - not exactly a name I'd associate with the Absolute"
"Its powers could prove useful. Especially if turned against Ketheric himself"
"Finding it may be easier said than done"
First BG2 Underdark video I found on YT:
"Things go well on the surface. The temple of their false god has been defiled."
"I am pleased. My revenge will soon come"
"We did not act for your benefit, Irenicus, though... you did offer some interesting opportunities"
"Yes, Matron Mother. Excuse my careless words."
"Our first prisoners arrive, Matron Mother"
"These two rank high among the surface scum, Matron. What is to be their fate?"
"Their presence sickens me. Kill them"
"So... I am in my homeland once again. Already I feel how unwelcome it has become. My eyes are no longer used to its darkness and my senses to the hint of the threat around every corner.
We must tread with caution, <CHARNAME>. There are, no doubt, drow in this place. Along with beholders, illithids, kuo-toa, and perhaps even worse.
The denizens here will expect no mercy and will offer none. If we are to survive long enough to find your Irenicus, we must be stronger than any of them"
If you can't see the difference in quality between these two sets of dialogues (of which, the BG2 dialogues were randomly selected, while the BG3 ones were specifically selected and aren't representative of the overall game at all, most of it is much worse than that), then you simply don't know what good writing is. That's ok, it's to be expected that not everyone has been exposed to good fantasy writing. But don't piss in my ear and call it rain. There is simply no comparison, either in terms of complexity or the variety of words used. BG3's dialogue is written by inexperienced and young writers who haven't been exposed to higher quality writing from setting-authentic works of art, and it's written for low-IQ low attention-span idiots who can't be bothered to read sentences more than 5 words long. In other words, it's written for the lowest common denominator, otherwise people will just skip it - they won't read it, and they won't listen to it, because it's 'boring'.
BG2 on the other hand sounds like people who actually speak like they're in a fantasy setting. Long, complex sentences are used. There is a high variety of vocabulary. There's this, how can I put it, roundabout way of saying things that evokes a long-forgotten/long-abandoned way of saying things. BG1 has its share of anachronistic moments, but in BG2 they really toned it down and kept it consistent. Even Minsc, who talks like an idiot, still has the style of speaking that is reminiscent of old fantasy stories, rather than this nu-fantasy speak that is deployed in every modern RPG.
It's a cancer that infects everything. Nothing is written properly these days, whether it's Larian or Owlcat, it all sounds like a fucking zoomer wrote it while slurping a coffee in their local Starbucks.