The biggest fallout from finishing 11th last season is the one we are seeing now: it is difficult to attract top-quality transfer targets to the club.
Martinez was very, very poor at man-management. He demoralised the squad, marginalised some good players (Distin, Eto'o, Baines) and benched quality in order to shoehorn his favourites in (Kone and Cleverley picked ahead of Mirallas; Del benched for the second half of the season). He signed some utter dross (Alcaraz, McGeady, Niasse) leaving the better players with too little support... he was a disaster and the proof of that was two disastrous seasons of abysmal results. The squad was good enough for a top six finish, but the manager was clearly not up to the task. Unsworth and Koeman have both got the same players performing much better.