It was good enough to qualify for the top 4 because as a squad we knew how to achieve it, the manager knew how to achieve it with those players and it was one last hurrah for a collective on its last legs. Much like Fergie's last United side were able to win the league at a canter but then fell totally away with the incoming of a new manager. When you remember the context of that season 71 points in itself is not a great total and Arsenal really should have finished 4th but they bottled it in the penultimate game against Brighton. So I don't know how much weight you can put into the 2018/19 results.
We are 2 years removed from that with a different manager, having lost all 4 of the key men you mentioned and replaced with inferior players.
I do think this side had the potential to finish in the top 4 this season if it had been setup correctly but that has nothing to do with what happened in 2018/2019.
I think we are in agreement - my point was just in response to some posters who seemed to me to be suggesting that our current squad was so fundamentally limited in ability that no manager could reasonably get them performing at top 4 level. Whereas I think with the right motivation, coaching and tactics a lot of managers could.