Koeman isn't just inheriting a poor squad, he's inheriting an inferior complex mentality.
I mentioned this on the players thread. 7 of the starting eleven were basically starters in 2013. 10 of the 18 were In the squad. The rest is made up of players who aren't good enough - Players surplus to requirements elsewhere, aging players, players who weren't exactly outstanding from lesser teams.
In 2013 we hired a relegated manager with little success notorious for bad defences and stubbornness. We then signed the spine of a related team. Apart from Lukaku we didn't really make any progressive signings. This mentality problem has lingered for years.
I haven't expected Koeman to be as lacklustre as he has been, and I expect better attitude from the players. But I'm honestly not surprised by these players anymore. Everyone competing has got rid when needed and replaced ruthlessly and we've been lagging behind in this aspect for far too long.