The first part of that is one of those somewhat annoying things people say - annoying because it is pure speculation.
A lot of clubs getting rid of a long term manager - ManYoo is a 'for example' - tend to do worse, at least in the short term. We can't know how we'd have done under a different manager so it's a pointless thing to say.
And does the squad need that much work? There is some dead wood to get rid of and we clearly near more up front but IMO we already have a squad which should be challenging, we don't need that much more.