Agree, I think they should've at least gave Mark of the Rift its own slot (like a ninth slot dedicated to MoR).
Focus abilities in general shouldn't have been in the same slots as the normal spells. They aren't used with the same frequency and their balance is completely different - it would have been just as stupid to stick the auto attack into the quickbar.
Practically every aspect of that UI is damn train wreck. It's actually worse than Skyrim's unmodded UI. At least that didn't ban you from re-jigging it during combat. It didn't even ship with the search items appearing in the radar - absurd.
Sometimes less is more.
Having limited options to choose from opens up for more types of builds.
Sure I'd like to have all my abilities available all the time, but in the end, I'd use only a handful (the most op ones) and then complain about the lack of gameplay/build variety in this game.
It's also the reason why the ME3MP was successful. While the pool of powers to draw from was limited, having just 3 powers at the same time opens up for very different gameplay types. Playing a drell adept is not the same as playing a drell vanguard because one single power is changed.
There is a *HUGE* difference between an interface that is minimal by design, and an interface that is minimal due to lack of thought. Diablo 3 is an example of the former. DA:I has DA2's spell system which was intended to work with 15+ options with Mass Effect 3's slot system nailed on top. It's like nailing a gameboy interface on top of an IPhone.