In your scenario they would need a huge amount of hashing power to actually make their own giant blocks
I guess you only need to construct such a specific block that takes forever to verify, not necessary a valid mined block, no hash power is needed
An economically rational miner wouldn't sit there trying to validate an invalid block forever... they won't stay a miner for long. They'll set their own limits and seek the longest chain of valid POW. They already mine short coinbase only blocks simply due to fear of orphan risk.