If it was a mistake, how the game now coming to Series S proving that? The only thing it proves is that split screen is a demanding feature and MSFT shouldn't impose parity of that, which they shamelessly accepted after the success of BG3. It's still a good console to play modern games, of course not at best fidelity, but I don't think that matters.

Edit: just realised you're saying that with an incorrect conclusion that split screen wouldn't be coming on Series X. Well, that isn't the case, and probably brings the game to more people with least amount of harm.