I don't want extreme but I do want a "slightly harder" version where the bosses launch straight into the second, more complicated versions of their attacks rather than starting off with a simpler demonstration version.

Also make individual mechanics happen faster, like the first boss of Paradigm's Breach doesn't need two whole lengthy turns to spawn copies and then label them 2 and 3.

And have individual mechanics have less warning or more thinking – to go to the example of variant/criterion, I like how the easier version of the Silkie fight has clear labelled left and right versions of its sweeping attack, but the harder version just has one named attack and you have to read the direction of it yourself.

Criterion fails, in my opinion, because it jumps straight to introducing unfamiliar and complex versions of mechanics, where I would prefer to get "the same mechanics without the training wheels". Criterion should have been this, and Criterion Savage the point where they introduced new mechanics entirely.