Google the "one button summoner". There are commands such as "/hotbar copy THM 4 WHM 1" which will copy your 4th hotbar for your jobstone-less BLM to the first hotbar of your WHM. (Can also write "shared" for shared hotbars.) There is also "/hotbar action "Glare III" 2 1" that will overwrite the 1st skill on your second hotbar with Glare III. Keep in mind players can have 200 macros.

There are drawbacks. Not being able to buffer your input likely means not keeping your GCD rolling. But the gains may outweigh the losses.

Evolved Mode is about so much more than reducing 123 combos to 111.

Since WHM is the only thing we know I'll use that example. WHM has two weaves that both mean "single target save": Divine Benison and Aquaveil. One is a 10% mit and one is a 600 potency shield. They're combined under Evolved Mode because they're both about as effective on a tankbuster or raidwide. (And the cooldowns/stacks were adjusted to make this a 1 second gain.) This is actually something they could have done right now in patch 7.5 and it wouldn't change anything for WHM.

And then there's whatever Mr Prime was doing with Dragoon lol. Actually trying to make that class unique and interesting.