Your logic is really not making any sense. Evidence of absence is not absence of evidence. Saying some people finished the game without posting problems does not mean problems didn't occur or that they can't.All evidence suggests it no though, as ever single person who has finished with this big has reported being over levelled at end game.
So no, it's not functionally broken. At all.
Show me actual evidence and I'll acknowledge it.
You keep leaning on faceless examples where the xp supposedly infected a player at the beginning and that it had no long term effect. You aren't providing anything to prove this is 100% the case.
I know the bug exists. I know what it does. I know I have it very early in the game. What I don't know is the consequences for 100% certainty.
So because of that for me and many others it is a progression staller. As no one realistically wants to spend 20-40 hours going through the game only to find out that their attempt to platinum is unobtainable. Or at level 19 you end up leveling up 4-5 levels at once and it overpowers you and takes you out of the experience(a problem someone just quoted). Or you want to just focus on the main quest but can't because you are underpowered due to lack of XP.
I really am not understanding why you are trying to white knight for CDPR over this? If this isn't a problem then CDPR should probably more in depth explain it instead of a vague answer and explain what is going on. Leaving people in a cloud of uncertainty that has paralyzed them from advancing too far for fear of unknown consequences.