[CryptoPunk]

That doesn't adrress my point at all. You can verify the requisite proof of work was done just by hashing the data in the block header to see if it meets the difficulty requirement.

The malicious actor cannot fake that. They have to produce massive amounts of proof of work to find a value in the nonce data field in the block header that results in that hash meeting the required difficulty, and even if the malicious actor delays transmitting the whole block, they cannot delay transmitting the block header, or other nodes will not even bother trying to extend their block.

So all miners can immediately verify if the block headers they are receiving have the required PoW behind them, and it would be very costly for a malicious actor to generate fake block headers with enough PoW to be accepted, while giving the malicious actor very little advantage in an attack, meaning it would be a completely impractical and ineffective way to attack way to attack Bitcoin.