You have to trust the "current state", if I want to join the network I can't verify it's correct. But if I have the whole chain I'm 100% every balance is correct
A masterblock is like the genesis block. Starting from scratch. So there is no difference.
Let's say I join the network. I get a masterblock from miners saying I have no bch. I have to trust them I can't verify that fact. But if I have the whole blockchain I can verify
The whole network needs to accept that masterblock like a normal block ;O also the miner needs to complete the hash puzzle in order to create the masterblock in the first place.
How about the argument that since a genesis block is only one block, and there can be an unlimited number of masterblocks, it is easier to verify the genesis block?