Changing the maximum block size would change the "energy used by a transaction" since block production is a factor of fixed time, not transaction volume, so the comparison is absurd on its face.
It's not a comparison. The fact is that the costs of processing bitcoin transactions are predominantly fixed. This tells us that bitcoin doesn't have economies of scale. The average cost of a bitcoin transaction doesn't decrease as the number of transactions increases. This makes bitcoin uncompetitive in relation to pretty much any other transaction processing technology.
And once that block size changes, the energy used per transaction will go down. It's really very simple, stop making it complicated. Blocks are there to hold transactions - that's their whole purpose. The fact that technically you can mine an empty block is an irrelevant detail of the protocol: bitcoin would not keep getting mined if there were no more transactions.
