Agreed though I don't know what the answer is. The current use of player amortization is not just inaccurate when it comes to estimating the financial viability of a club it is actively misleading more often than not.
The big problem between the Premier and Championship is the gap in income so that when a relegated club comes down it either goes bankrupt if you don't support it financially or it gets a massive financial advantage over the other clubs from being supported. Smaller gap and the problem goes away.
There is an argument that you should just let people spend what they want and if a club goes bust, it goes bust.
In the US, you have a closed shop model which, ironically given the country, acts more like a socialised model of sporting finance. They solved the issue of relegation by not having it. It also makes for reliably good profits for the owners so it's hardly any surprise that various owners here would like to recreate that model.
I don't think you can solve a problem that is caused by a huge gulf in income disparity between the Premier league and the Championship without reducing the gulf.
If you go with wages to turnover, it's fine in the Premier because most clubs will be able to hold the line around 70%. In the Championship, as it is, we struggle to hold the line at 100%. Maybe you could do something like 70% wages to turnover but an owner is allowed to donate up to a certain amount, say £10m per year to count towards turnover. I think they may do something like this in Spain. Anyway, I won't pretend I have an answer but I do think that FFP/PSR is simply not fit for purpose and I strongly suspect that there is no way to tweak it to make it fit for purpose.