I agree with most of this. I think last summer was such a colossal cock up because Levy was so focussed on delivering the stadium on time and so it should be a one-off.
But then there is the broader concern that almost out of nowhere, teams like Everton, Wolves, Leicester, Wet Spam and even Fulham are beginning to spend serious cash compared to us (still peanuts compared to City et al.). There is an admittedly miniscule pool of players out there who could improve us at the prices and wages we can afford. Until recently, the only competition we faced for their signature was Arsenal and Liverpool. The transfer battles we had with the latter became the stuff of legend. But now realistically we face competition from half the league, that's how much money there is sloshing around and that's how desperate owners are to dine at the top table of the CL. So now players we are often heavily linked with are ending up at rival clubs and that initial pool of talent is shrinking by the year. Not going to bother listing them all but i don't recall a summer where so many of our supposed links went elsewhere. Seri, Gomes, Keita, Mawson, Pereira, Tielemans, Maddison...and that's just one season off the top of my head.
Sell to buy no longer works because not enough teams care to operate that way.
As you, I and many others have said multiple times, the odd outlay of £30-40m here and there really isn't going to make the auditors blink anymore. I get that a marquee signing in the £70m+ range requires a clear out first, but currently we're stuck doing neither because clubs bigger than us will always catch the marquee fish first and clubs smaller than us have started nabbing the smaller ones first too.