Want to fix arena?

-Increase everyone's HP by 50%
This will fix the problem of people getting insta-gibbed and will nerf the speccs that undeniably need to be nerfed (Ret paladins, feral druids, destruction warlock). The side effect of this will also be nerfing comps that are obscenely burst-reliant, like Priest/Mage/Rogue.

-Remove professions in arena
Anyone enjoy playing against people who have the hand-rocket, lightning generators and rocket boots only to lose because of either ridiculous burst or because people can get away from you when they shouldn't be able to? Yeah, me neither. PMRs are also notorious for utilizing these tools and winning many matches simply because of it (see teams like Affix's PMR, where I'm pretty sure all 3 players are engineering and will drop someone from 100% to 0% in literally 2 GCDs).

-Nerf Mana Burn
With Priest's mana longevity as high as it is now, mana burn needs to be addressed. Now arguably the healer with the most longevity in the game, the priest should not also be the most offensive in the game.

-Remove Vindication
This will also reduce the number of debuffs ret paladins can apply but will address the primary problem that ret paladins just do way too much unpredictable burst damage.

-Remove Unrelenting Assault
We get it, warriors were really bad last season, but did Blizzard really need to add a 75% healing reduction?

-PMR must die out
I feel like this one really deserves some serious attention from Blizzard.

If every comp in the game had the durability to survive an expansion pack and 5 seasons, then the strength of PMR could be justified. Unfortunately, every other comp in the entire game goes through phases (IE: patches hit and a lot of the FOTM comps phase out), yet PMR has been able to sustain its power. From a third party's perspective, it seems fantastic that 3 players can play one comp for tournament after tournament, patch after patch, expansion after expansion.

Problem: if one comp can be powerful indefinitely, then the legitimacy of tournaments become jeopardized for the reason that teams that don'trun PMR have to constantly adapt to new patches, seasons and class changes while the PMR teams can constantly build on their comp and get an innate advantage by nature of having more experience time. Trust me, if I could have run one comp for 5 seasons, I would be invincible, would have a 99% win ratio and be able to take down every team in the entire game. Unfortunately, that isn't the case, and I, like every other WoW player that doesn't play PMR, have to constantly be dealing with the hurdles of FOTM comps being nerfed.

Kill PMR. Force these priest/mage/rogue players to be innovative and create a new comp just like the rest of us are always having to do.

-Remove all proc-based trinkets that release burst damage
I can't even begin to understand how Blizzard intends to address burst damage (from all classes really) in the future without first addressing this. Having 2 rogues open on you with those proc trinkets, lightning generators and handrockets will lead to even a paladin going from 100% to 20% before the cheapshot even wears off.

-Remove the waterfall on Dalaran Arena
Don't think I need to explain why on this one.

-Remove the fire on Ring of Valor
Same as previous answer.

-Make the pillars on Ring of Valor permanently up
Refer to previous answer.