I am thinking predominately about roots and snares here.
Frost mages, for instance, have a snare component to most of their damage spells. There are also proc chances for spells to root.
In my opinion, this should not be a thing. A spell should either deal damage or apply a snare or root.
It should be a choice the player makes, between spending a global on a snare or on a damage spell.
Like frost mages again, they could have a button that turns on snare effects on their spells, while also adding a reduction in the damage output. It would add an element of skill to it, rather than just applying 50-90% slow on every spell cast while bursting.
Warriors can spec into bladestorm so it slows targets hit by it. That should also reduce the damage it does.
Same goes for stuns. A spell should either stun or deal damage. Not both.
Another insane example is devoker, that can keep their target permanently slowed to 10% movement speed, while having nearly 100% uptime on hover, allowing them to cast while moving.
They also have a high damage aoe spell that also stuns all targets hit by it.
Rogue is a good example. They have many stuns, but none of them deal damage. So you have to make a choice with each global. Either stun, or deal damage. That adds a skill element to it, which is good.
I don’t know if people remember an old verision of ww monks fists of fury, which also stunned targets while hammering them with big damage. It was reworked, since it was just too stupidly strong.