FpicFail, your memory serves you wrong. Gaining our mana back with AotV wasn't nearly as easy as you make it sound, unless someone innervated me.
Blasting my mana away was part of key cooldown windows, outside of that it was important to not starve yourself.
PvE is also only half of the picture as PvP was much prominent back then and mana was great for it, as you could unleash when you needed to. Right now I can't unleash shit, I literally do my standard rotation.
I think mana wasn't perfect, but at least it wasn't fool proof. Let's be honest here, what do you need to think about when playing MM right now? Sidewinders is basically a requirement if you want to be competitive, so all you're actually doing is trying to fit as many Aimed Shots in your Vulnerable window and using Marked Shot at the proper time. Outside of that you can't go wrong, you can't botch your rotation and resource starve yourself for the whole fight. It's just such a safe spec, like all Legion specs.
I don't really mind too much though as I'm 10 years older now and I can welcome the faceroll, that all classes are at the moment, but I also can't close my eyes to the fact, that all specs are fool proof right now and even talents are one dimensional. You want better ST dps? Pick this talent. You want better AoE? Pick this talent. I mean people complain about talent trees, but the current talent system is even more brain dead than the previous one.