At least the absurdly broken parts.
Design Problem 1, Broken damage: Some skills do WAY too much damage, as in two or even times what they really should be doing. Nobody should be 1shotting anyone from 1200 range or making the old chill reaper look like some discount free to play build.
Problem: Broken damage with too much sustain, cc and support ability. Constantly nerfing cool-downs/life force wont do anything. Scourge was always pretty bad even during early days if you didn't run sand savant.
Possibly repeal a few changes like Path of Corruption and dhuumfire...
Problem: Hammer damage was put stupidly high, compounded by how ridiculously easy it is to self buff yourself to 100 crit chance and 25might.
Coalescence of Ruin
Problem: Winds of disenchantment is no question an overpowered elite, but for some reason I don't really want to nerf it.
Winds of Disenchantment
Problem: Really more of an Spvp problem than a WvW problem; damage spike is a little too high.
Design Problem 2, No viable alternative to firebrand which kills diversity: Firebrand is basically the old boonshare mesmer, tempest healer, rev resistance bot and healer combined into one. Simply nothing comes even close to being as versatile. Lots of suport classes can heal but can't do jack as far damage mitigation and boons (especially stability).
Problem: Too much support relative to other healers (druid, ele). To be fair the problem is that other ele/druid dont offer any form of aoe stab or damage mitigation so you will always have to fun a firebrand no matter what. Still, tomes are too powerful and have no business having comparable cool downs to virtues. If we're going to have dedicated healers, then firebrand should be somewhat interchangeable with ele and druid.
Tome of courage
Tome of resolve
Problem: Offers great healing but doesn't give out critical boons. Should recieve some very generous buffs to support. These changes will only apply to wvw because they would destroy pvp balance.
Search and rescue
Problem: Offers great healing, but same as druid it needs to be able to grant boons to compete with firebrand.
Feel the burn
Eye of the storm