I agree with your post on how the void years' work.
The downside is when contracts are not extended, whether by FA, traded or retire.
Example for the Eagles this coming year, Kelce and Cox retired, and they have a $25M dead cap hit.
The day does come when you have to pay for players NOT on your team anymore.
The Eagles have taken on this risk and so far, they have done pretty well with it.
The Browns, on the other hand, have done the same thing BUT are facing a horrible result.
I see the "Void Year" option as a useful tool but not a panacea for the cap.