What do you mean, “underbidding”, e.g. “underbidding attack”? I don’t understand this term in the context of your hypotheses which assumes a perfectly efficient market for hashpower
Suppose that it takes $50 of energy to find a hash at current difficulty. Transaction fees are at $50 (in BTC). I can offer miners $51 for their hash power, but they might be suspicious. So the other thing I can do is confirm transactions for $49 in fees, which I'm calling underbidding. This will drive miners out of the market.
Wouldn't this mean you ignore the transactions with the higher fees for the other miners to pick up, thereby making mining more profitable for them?
How bitcoin transacting work is not that the miners publish their price and someone accepts that price and thus sends the transaction to that miner. How it works is that you publish your transaction with the fee you're willing to pay and if your fee is high enough, it will get included in the next block.
