I was just wondering where you went pal, as I hadn't seen you post for a while.
Onto your points -
1&2) I think it's clear that whoever is in charge, the incompetence and toxic nature of the club (ie the hierarchy) will always bring you down. Poch, EtH, Pep - whoever is the man in the dugout he'd be working under the same conditions i.e. an incompetent duo in Murtough and Arnold, parasitic leech owners such as the Glazers, and a budget that will be diminishing year on year. The players are rejecting us because we have idiots running the club. EtH has his targets and we're failing to get any of them - that's not on the manager.
3) I think EtH is very adaptable based on the systems and formations he tinkered with in Ajax. But again it goes back to recruitment - you need the right type of player to make the right idea work. If you have the right idea and the wrong player, you're starting hamstrung.
4) Again - it's not to do with player egos. The background / board room / club structure / hierarchy is a toxic unmitigated clusterfeck. That wouldn't change if Poch would be in the dugout.
5) Yes, Poch does know the league well, but I don't think this is that important. First time managers to the league have been a success, and managers who've operated in this league for decades have been poor. It's a non-factor.