Decouple attack speed and animations for certain skills.

Okay, you're probably thinking two things and they're along the lines of "What does that title even mean?" or "This isn't your thesis, is it?" One of these questions will be answered.

But first, let's explain.
Fast attacks are fine, you can throw them out, you have a small amount of time to get stunned by an enemy and usually you can time it better, and if you get stunned it's no big deal, just use the skill again.
But these slower skills can cause an issue. The animations are super long because the attack speed is very low. 50% attackspeed is rough, but these types of skills should exist. It gives variety, and that's where the decoupling comes in.
A new stat, called Animation Speed for certain abilties, so say you have an attack that takes 1.5s to complete, which is too long to be useful unless you have attackspeed. There are supports that mitigate this, like Hit and Run, Unbreakable, etc but it often feels bad to use these supports.
So instead I propose that this theoretical long attack still can be used every 1.5s, but only takes say 1s to complete, giving you 0.5s of free time to use something else while you wait for it to come back, like a soft cooldown.
This lessens the brutal slowdown of some of these long skills, so you can dodge or continue throwing out other skills.

Blood Hunt: This isn't a slow skill, but it feels like it should be, It's a combo finisher and helps clear nearby mobs. This could be a quick finisher attack or a proper cooldown skill.

Cull the Weak: Also a finisher with a clear purpose, to get frenzy charges. Forced movement skills are also rough because of travel time and you're not phased while using them (Even though I think you should be)

Marks: These should be super quick since the animation is just a hand gesture, and attack-based builds only have supports to increase cast rate. The input of the player to want to mark something is important, but having to wait 0.5s on base can slow down combat quite a bit if you're reapplying marks.

Curses: Same thing as marks, but in this case a fast speed but keeping the actual casts per second is important, so you don't immediately curse everything.

Banners: 1s Use time for banners is the reason why I never use mine. This doesn't come under the mentioned category since it has a cooldown but nobody wants to sit there for a second planting a flag when monsters are running at them.

I'm sure there's other skills, but these are the ones I have actually used, I could speculate on others but I don't think that's fair without trying them. I have played merc and he felt fine though, since there's reloading. That's your time to do other stuff.