>"Crypto performance doesn't matter"
the argument I was trying to make is more in the sense "is it worth to take (even a minimal) risk optimizing performance given that this very performance gain is not (that) important overall"
That being said, I do understand that there are a lot of areas where performance/energy budget is tight and this actually makes a (huge) difference
"We could have doubled the speed of this hash if we had been more rigorous about security margins" seems clearly to be a powerful claim. Especially since performance is in reality a pretty huge part of how we choose the cipher designs we standardize.