We can speculate on the detail, e.g players who should be bought but the fundamental fact is that the poor strategic thinking of the chairman has resulted in the current situation.
He should have lined up a top class replacement for Robson months (or even a year) before getting rid of him, rather than find himself having to plump for 4th choice.
Souness comes across as a pleasant, reasonably intelligent, articulate person but unfortunately appears unable to manage/coach/motivate the players under his charge, as well as making some very poor expensive buys.
Surely Shepherd must be looking for a replacement now (and maybe has been for some time?)with a view to installing a new manager when available,also Souness and the players must by now realise that his time is numbered.
A resultant problem is that of even greater demotivation by Souness, the coaching and playing staff. This could result in a downward spiral that could lead us into the relegation zone!