You're fighting a strawman. The most common argument I've seen is that the player character (if they're not an origin one) FEELS like they're not as important as the origin characters. Of course other games have npcs with backgrounds. No one is saying they don't. They're saying that the player controlled characters feels more personal to the player. Right now, the origin characters in BG3 feel like developer inserts and the actual player character just feels like a punching bag that has to earn the favor of the dev inserts. We get it, other games also have npcs with backstories, that's not the argument I've seen anyone put forward.
Also, you keep saying "it's EA" but the fact is, we paid money to participate in this EA, we're very much allowed to comment on the current state of the EA, and from my experience, EA DOES give a very close approximation of the developer vision and how the rest of the game will go. I've had very few EA experiences where the general feel of the game changed completely from EA to release. The fact that this game already feels similar to the first act of DOS2 lends more weight to that and the statements from the devs themselves about how we'll have to choose our companions before the end of act 1 is even more so.
That said, I respect your right to an opinion and I dont intend on this coming across as insulting to you (text sometimes makes things more aggressive than it was meant to be :))
I do bring up EA, and while it is, the point is more when players are comparing what we have to games they've finished. We're barely scratching the surface of whatever the full game's going to be, so I don't know where my character is going to go narratively, yet. I'm not insulted, we don't have to agree. Forums would be really boring if everyone always agreed on everything.
But more to what I'm looking at, in NWN I wrote a novella describing a character's backstory before it got into the module I was running it in. Fan fiction is cool, but when I wrote it, I was running a new level in the module with another player that I didn't know, and when they asked about why I was spazzing out about Drow, I had to write the barebones origin on the spot. I later fleshed it out, but if my character had had Geralt, or even Warden level definition, it wouldn't have been possible to do. So I really like that a Custom character is a blank slate, because if the spirit moves me, I can come up with my own, and make it more interesting, possibly. Some fan fiction is better than others, after all.