As much as it pains me to say it I am now of the thinking I had when Gerrard first came in.
We need to improve the squad / starting 11 every window but it won't happen in one transfer window in the summer.
As much as we are all compiling lists of the players we'd like to see go and the 5-6 we'd like to see stay its not doable in one window especially with limited resources.
From the current squad there is 15-20 players people would want rid of and realistically that just isn't going to happen.
You're certainly right as far as paying transfer fees goes, but here's the thing that's most depressing about your "won't happen in one transfer window": We should now be several windows into a rebuild. Instead, our dealings in recent windows have left us with very few players who have been upgrades or even adequate replacements for members of the 55-Seville team who have left, retired or need to be moved on this summer.
Of the current squad, the only players brought in since Seville who I think have been unqualified positive additions are:
Butland (certain to be sold in my opinion)
Yilmaz (left back)
Souttar (squad CB)
Sterling (midfield, maybe RB if Tav goes)
Diomande (maybe, midfield)
Cantwell (an option at number 10, far from first choice on my teamsheet though, would sell if we can get better)
Sima (left side of front three - but not yet our player)
Danilo (maybe, wasn't fully convinced prior to his injury)
McCausland (squad player)
Cortes (looked handy, but a risk given his injury and our track record with injuries - I feel the money will be better spent elsewhere)
For me, those are the only players who have come in since Seville who deserve to be in the conversation to stay next season.
Of the 55-Seville era players, the only one I'd hang onto would be Tavernier, and with several caveats - no longer guaranteed a start, no longer captain. That may not be what he's looking for, so it may be time to part ways.
I would certainly sell Dessers if we can get a decent offer. But at a push, he could stay as a backup striker - for all the slagging he takes, he has scored goals and done a job at times. He just can't be relied on as our first choice number 9.
That still leaves us with a huge rebuild including a first-choice goalkeeper (assuming Butland leaves), most of a defence, a leader in midfield and one other first-choice midfielder, and a first-choice number 9. And then backups. And then we have to buck recent history and make sure our recruits are mostly success stories rather than injury prone duds - otherwise, we'll be back here next April with another new manager calling for another clearout and warning that this will be a slow rebuild requiring several windows.