I don't think the summer overhaul needed is quite as major as is being made out. At the end of the day, the squad we have now has qualified for Europe 4 seasons out of 4 under Emery. Champions League at least once, hopefully twice, a Conference League semi-final, and Europa League final (hopefully winners). We're a good side.
Plus, it's perfectly normal for players to be still playing at a top level through to their mid 30s (34-36), so players like Matty Cash or Ezri Konsa - both 28 years old - will have a few more seasons in them before we have to seriously consider replacing them. Most of the players hitting that mid 30s range are squad players, so replacing them with younger models (which I assume is what Olabe has been brought in to do) is the right thing to do as far as I'm concerned. Get in younger players who will be happy as Champions League squad players with the longer term aim of transitioning them in to first team regulars, whilst the current (older) first team players drop to more of a 'squad player' status.