None more?
Let's look at United honestly. They had the world's greatest manager, loads of cash and success. The Glazers came in, leveraged buy out, dumped the debt on the club...and they continued to win.
They began to lose when the worlds greatest manager left and he was replaced by someone that couldn't immediately (or, to be fair, ever) replicate the wonders of his predecessor. So they sacked him and brought in a manager that had never coached in the Prem, and was at his peak in the 90's. United's on field or off the field success has nothing to do with money. They spend as much or more than anyone not named Real.
If they hadn't gone down that route would they have sold Ronaldo? Maybe not, and maybe that would be a difference. But we don't have any idea of that for sure.
Debt, in real terms, is meaningless if you can A) continue to make your payments and B) not alter your spending habits while continuing A.
Basically, United and their ownership is meaningless in the context of Everton. We are not kings of the footballing world, with the worlds greatest manager and some of the worlds most marketable stars. We couldn't necessarily survive the sort of leveraged buyout United have. But at the same time, we shouldn't pretend like the ownership group is holding them back. The managers and players are holding them back.
I agree with your point that a leveraged buyout is dangerous, and could be very bad for Everton depending on the way the markets go, but that does not mean the Glazers have failed United (yet, obviously since there is still debt, there is still the looming spectre of a market burst and United being in a bad place...but so long as the television money and sponsorship money is going up...it's very little material harm done).