Both him and Pedri are replaceable at the moment. They're just part of the XI when they play. Better than their subs, sure, but they're rarely making a big difference.
That said, both of them have the potential to reach that level. The question is how much more they are going to develop.
That's naive. I mean we all agree that our team is dysfunctional (virtually no frontline and a weak defence) and our coach mediocre, but somehow our midfield should carry us? Who do you think would make a difference in this team? Kimmich? De Bruyne? If you believe that, fine. Otherwise the criticism is over the top.
Frenkie played 9 games so far, his first 3 were phenomenal, Valencia was a mixed bag (invisible first half, good second half) and in between he was average. What's the expectation here? Carry us 8/10 times in a hectic schedule with international breaks? I would only expect prime Messi to do that.
I think we forget here that modern football requires 11 good players with well defined roles. We have 9 at best and heavily depend on Ansu and Dembele coming back. We will see where we stand if they fluke to stay fit and our midfielders can actually play like midfielders. I reserve my judgement until that day arrives.