My problem is that the game kinda signals that it's trying to be Dragon Age, with its free and open protagonist, as opposed to the more defined Mass Effect and Shepard. I think it ends up taking the worst of both worlds frankly.
I absolutely agree with you about PoE. I did multiple playthroughs of both PoE1&2 and managed to roleplay as very different characters, with different background goals and ideologies and they all worked really well.
We will see how BG3 will end up looking at the end. I am still pinning any issues with protagonist and companion writing squarely on the shoulder of origins - you can have blank protagonist. You can have a shared protagonist like Shepard. You can have predefined protagonist. You can have a group of protagonists. Really you can do whatever you think suits your game best. What Larian tries to do, is to do everything at once, and I just don't think this is a feasible goal.
PoE was an exception built from the ground up for that though, so it's a bit unfair. I mean, you could choose who the person you're looking for is from your past (sibling, lover, parent too I think, etc), and that was a constant theme. It was like a literal build your own story simulator instead of you inserting yourself into a preexisting narrative. It imo suffered in other aspects because of that though, such as the main story itself being really loose and unfocused to accommodate this.
I also disagree about Shepard becoming their own person. They were very much a generic middle ground self-insert character that the writers unabashedly leaned towards paragon. Renegade options are all really awkward and 90% of the time result in the same 'good' outcomes outside of specific major choices that are really just story branch toggles than anything else. Not really sure what you guys are considering memorable specifically about Shepard's presentation/writing, and I'd love to hear examples, because I remember Shepard being pretty bland by intent so you could have "your own" Shepard. Compare that to, well, literally anyone else in the cast who was keenly influenced by their history, personal motivations, and mistakes/successes.
Or, you know, compare Shepard to a true fully developed protagonist like in, say, God of War. Kratos' identity as himself is what carries every shred of that story, from his past to his troubled life with his son, to all the consequences of his past actions. That story wouldn't have worked as a "make your own character kind of game," and those are all the reasons he's considered incredibly well-written by many.
You're just never ever going to get that with a self-insert character. Shepard was ultimately designed to merely represent the kind of Shepard we wanted to be. I suggest you look at some retrospective videos if you're ever bored; I love watching breakdowns of plot and so on, and quite a few of them do an excelletn job at breaking down and candidly point out just how flawed Shepard is as a character and how mostly meaningless the paragon/renegade system was. Our love of him came as a porthole and method of influence into the surrounding narrative and companions, and that's what we mostly remember fondly. Our adventures through Sheperd, not Sheperd himself. That's imo what games like this are really good at and why it works well enough for many rpgs to do the same, just like BG3.
You can't really have a player created self-insert character with a strong personality and highly developed presence. It just doesn't work that way, and that's exactly why Tav has so few lines and the narrator is front and center.