Anyway, can you say at least one real argument against removing RS under checkpoints ?
It isn't possible to independently verify the chain. This significantly elevates the trust model for checkpoints from choosing among valid chains to trusting that the chain below the checkpoint was valid before being trimmed. Again, tradeoffs....
The chain is verified by the fact that the block hashes are immutable. An attacker can't change the transaction data by even 1 bit and get congruence with the block hash history.
It is only a risk against an attacker that has 50% of the network hashrate and thus can rewrite the chain, but in that case you have bigger problems any way.
Thus afaics, TT's concern is BS.