I agree that it wouldn't work for jobs that have split combos, as mentioned, or for monk's complexity.
But for the fixed combos, hell yes! PvP bars are much better also because of that. And why does it feel like you're doing less just because you're pressing 111 instead of 123? You're not doing less, you're just reducing bloating and optimizing the space. You don't have to be a better player to press 3 buttons in succession instead of 1 three times.
Just thinking of for example RDM melee combo, it's 3 buttons you only use a bunch of times in a fight and only in a specific order, what's the use of them taking 3 slots?