>You can still amortize the cost of the block across its transactions

Sure, if you're more interested in talking points then useful metrics. Increasing or decreasing the block size limit would lower or increase the "cost of a transaction" (since blocks are generated on a schedule commensurate with difficulty, which is roughly a function of how many miners there are) without actually changing the amount of power consumed.

What you're doing is basically correlating the world's average temperature versus the number of pirates and declaring that pirates are responsible for global warming. In reality, the two variables are unrelated and not even correlated.