I really don't understand what you or Andresito for instance have against it being used the way it is now i.e. in 10% of the fixtures to find solutions when banging your head against the wall with a 4-3-3 isn't working because 90% of the team is out of form. Orthodox 4-3-3 with sodall deviation depending on select names is the worst thing you can do to a team. See Pep's blockheaded approach.
Just saw this. I must say I haven't followed any discussions here at all.
My problem with 3-5-2 is the intention of Koeman. We won with it against Valladolid, a very weak opponent, and Koeman thought "wow, I just found our go-to formation".
It's useful in certain situations, against certain opponents. I am 100 % of belief that it doesn't work in the long run if you want to challenge for all titles.
I have no issue changing to it in game or using it in extreme cases, like the 6-1 vs PSG.