There's no way that a better manager wouldn't get more of a tune out of these players, even with an unbalanced squad.
Vlasic, Lookman and even Mirallas can all play wide, so we could start with a balanced team if Koeman wanted to, but he chooses not to.
There's no reaction from the players after all these bad performances. We're not coming out and reacting, which suggests to me that Koeman isn't getting any sort of message across.
I'd go all out for a Tuchel or Ancelotti, and if that didn't work out, I'd give it to Unsworth for now. Lots of clubs promote a talented youth manager from within. It's not unreasonable or unheard of at all.