Back then there were many cancerous mechanics like cast slow debuffs, sacred cleansing, PvE items, bloodlust etc. that we don't have these days. Unfortunately spam-able CC is still here, and when it's used effectively at the highest level it's unbeatable. It has been like that for like 2 years now. When Mages were glass cannons back then and dispel was spam-able that was all fine (when poly spam was essential to their survival), and to be honest it was very likely you had equivalent horse shit mechanics on your team to make it fair.
It's not needed since they are "Steel Bazookas" now. (Maybe make ice barrier/temporal a thing again instead of flame glow).
Inb4 argument: "YOU CAN KICK SHEEP LOL".
The 50% MS obviously encouraged Melee/Caster/Healer more than it does these days. The downside is many comps would be without it that would probably need it to stay remotely competitive.
My suggestion (knowing it will be controversial) would be to give it to every single Melee. Remove it from Combat Rogues and Hunters. Put spammable CC on a 4 second CD. Put Mage and SPriest purge on a 4 second CD too. Revert the focus cost nerf for tranq shot and fix bestial wrath so it doesn't reduce tranq shot cost (same effective BM nerf without obliterating surv/mm). I feel like this sort of homogenization would promote different compositions instead of having a very narrow meta game which is all they have managed to produce so far with their efforts.
Oh yea and take away everyone's current lay on hands. Go ahead and make it up to them in other ways. It would promote defensive play instead of being all "NP out of this I will 1%-100% you".
Also thank you AJ auto saved content feature
let's stipulate, for example, that melee would have a 30% healing debuff and casters would have a 20% one. in this situation:
the utility and control gained from wizards would come with a less significant healing debuff
kitty cleave and other nonsense would still have a potent 30% debuff, but still not as powerful as melee/ranged/healer
this way, you'd never really be able to complain about two melee training a DPS to stall the game until dampening and then switching to a healer or the most popular complaint, wizards running away until dampening is thick. melee/ranged/healer would inherently have a healing-mitigated advantage on whatever target they're on, the entire game
it should be noted that back then healing debuffs were the among the most significant aspects of arena and the game was tuned around having them active all the time