Volo is, if I remember correctly, one of first original characters created back when TSR adopted the Forgotten Realms as an official setting back in... Middle of the 80's I believe? I remember he wasn't actually created by Ed Greenwood but one of the TSR . But regardless he is one of the most iconic mascot characters for the setting.
The bard sidekick (comedic or serious) archetype is itself a very common character in writing. Accusing characters of the same archetype for being plagiarized just because some new hip work also features that archetype is foolish and only showcases how ignorant you are about the greater world and history of literature that makes up the foundation of our cultural heritage.
In short, it's like accusing a hypothetical new Blade adaption of being a rip-off of Twilight because they both feature vampires (despite both deriving vampire tropes from even older works). Even without the faulty chronical ordering the idea itself is ridiculous.
My point is that if we talk about Volo and dandolion, the fact that Volo is the original is completely irrelevant here. Unless Larian can do anything new or interesting with him, he will always be (at least in the context of bg3) a less cool dandolion copy. And the big thing here is that unlike Elric for example, Volo is not a super important character that you can't build a forgotten realms story without. So the decision to add him in is worthy of criticism and comparison to dandolion
Volo appears in both BG1 and Throne of Bhaal, and also provides commentary in the game manuals in the style of his "Guide to" setting guidebooks. He is also the framing device used for NwN2: Storm of Zehir. He is very much one of the most common poster boys of the setting and is still used as such by WotC.
I mean, I happen to loathe him myself. But this is hardly the first or the last work they've forced him into. He's basically the Wolverine of FR. No story needs him, nearly every story is better from him not being involved, but you'll be damned sure he's going to show up in nearly every story anyway.
