Your tone here is one of unbelievable arrogance. You 1) ignore the fact that the UTXO set still has to be computed, and hashed, which requires someone to have all of it. 2) That you still cannot actually validate it without having all of it. 3) You literally hand wave away fundamentally changing everything about Bitcoin’s validation and trust model as if its not a big deal. Your proposal literally is not a solution to this problem in anyway whatsoever. It is a mechanism that facilitates nothing but users not validating and thinking that magically somehow just trusting miners/mega-nodes is the equivalent to actually validating the state of the UTXO set. It is not.
This is exactly the problem. People like you who think “We can solve things by moving data and using hashes” just fixes everything. The model is validate. If your solution to the problem of validation costs is “don’t validate, just trust this thing people promise in this hash” you have solved absolutely nothing.