One rather significant difference is that Pep is the second most decorated manager in PL history and the other has won the SPL.You could take any current manager in the PL and likely championship, put them in charge of Celtic, and they will deliver you the league. It’s much, much easier.Sorry this is the team that everyone expected to win the league at the start of the season, they're currently on a run on 1 win in 14 matches with one of the best squads in Europe and the best manager, I sorry what have I missed?
There's actually a lot of similarities between Pep and Ange notably that both managers are stubborn and won't change their philosophies, Pep could easily get them to sit in a mid block and cull the pressing and they would be winning more matches, Ange could do something similar...both in that respect are doing terrible jobs.
You stick with Pep because you have empirical evidence that he is the best. Ange has done nothing to warrant that faith or comparison.