I think this is a really good appraisal of the underlying problems with pvp in this game. They've made a few decent changes over the years and introduced some interesting modes/rules, but core issues with the engine deriving from it being a pve-first game hold it back from ever being great, the fairly long GCD and server tick rate chief among them. Re: healers, they've always been the mvp role but it was only with the 4.0 changes that they became godly relative to the other roles. The other roles got a reduced ability to melt them and it really focused the gameplay down to everyone else coordinating their attacks on the healer at certain intervals when their cooldowns are ready to burst. For most people it just wasn't fun and I noticed widespread complaints about healers on the official forums, reddit and gamefaqs at that time. The really hardcore pvpers pushed back and basically said get good, the game is fine.

Well the complaints mostly stopped because a lot of people just stopped doing pvp. It was only fun for the people at the highest skill level. I can't confirm because I don't use addons, but I suspect those are a factor? If a person had a tool to force their skills into the same data packet and align with server ticks, that's a huge advantage in this type of pvp to assist coordination and bursting healers at the exact right moment. Casual players who don't cheat cannot access that kind of assist. I hear that addons can also read the opponent's attack before the game displays the cast bar, which might make it possible for Silence to be reused reactively rather than predictively. Again a fix to the unfun design that's only available by cheating.