The fact that you personally dislike swear words does not translate into the writing being bad or "quirky". You're simply trying to pass off your personal taste as some sort of objective criticism of BG3's writing quality.
I am usually against swears, but there are two games where swear words felt on point for me was The Witcher (the whole series, actually) and [PROTOTYPE] (the Web of Intrigue has some characters swearing, and quite a lot, in fact). But that's probably because the delivery was perfect so the whole dialogue felt natural as a result.
The "alack, thou hath cometh for a quest, brave knight" shit always seemed like a failure of imagination in fantasy settings to me (sorry Richard).
Interestingly enough, there was a different language used in the court of England (French) and the common folks were using something completely different. The "high and mighty" manner of speech can have some sense in that context. It usually is not too entertaining. However, I did like Vampire the Masquerade: Redemption's approach; adding an "old word" here and there in the medieval era. This also provides great contrast when Christof awakens in the modern era and Pink the Punk is his companion who explains the new world to him.
Imagine how much the Elder Scrolls would suck if all the Dunmer were like "thou hath come to yon land of Morrowind, traveller, and we doth not take well to outsiders here". It's way more fun to have them run at you yelling "STOOPID" and a bunch of made-up slurs.
N'WAH!
I would argue The Elder Scrolls didn't need old medieval manner of speech, because races had different ways to highlight their cultural differences. Dunmers have foreign words thrown in here and there, Argonians and Khajiit have different perspective, while Nords and Orcs have their own mannerisms in the way their speak. All in all, I think it was the best possible way of doing this.