tl;dr - mez is heinously fucked in PvE currently, esp at high end
Let me start by saying that I understand why this change was put in, and that this is a PvP server and most changes have been made with PvP in mind, but I don't think this one was particularly thought through or tested much as of yet. Being able to effectively act as a bard or enchanter in PvE requires you understand and roughly keep track of how long something will be under your CC for. If 4 adds come into camp as a bard, I cycle through them with mez, and if I've timed them right, the mobs stay CC'd. The only caveat is when there is a resist, at which point you have to make a decision to try to CC that mob again or move onto the next in the pack (assuming there are 4 here) knowing that this one that resisted will run free. This works relatively the same for an enchanter. You throw down your mez's early and keep track of when they are approximately going to run off and redo them a bit before, leaving room for resists. This is how things have been CC'd for the entirety of Everquest. It's a fundamental mechanic of the game in PvE, the bread and butter of why enchanters existed and were played. You could predictably remove certain mobs from the picture.
Currently, the partial resist system turns PvE crowd control completely on its head. Without any resist messages on partials, you have no idea when anything is going to cut loose. Crowd control becomes a total cluster fuck.
In the bard example, you might as well tear your hair out because any one of those 4 mobs at any time are probably going to be running all over the fucking place. Enchanters might be in the middle of a SLTW recast when the mez breaks, which means that you won't even be able to react (because you cannot cancel your own spell cast) for maybe another 5 seconds.
In some circumstances, mez becomes so unreliable that it's almost a liability. Why mez something that you are now pretty sure it will run and beat on SOMEONE for a few seconds before you're able to react? Your only option is to chain cast it on one mob every few seconds, otherwise, you'll have no reliable concept of keeping something locked down.
The problem with this became apparent when I was in Hate the other night. I had a single mob in camp that I was chain CCing with my bard. Just sitting there with mez pulsing on it. I saw zero partial resist messages, yet it was running all over the place the entire time. It just killed one person after another after another. All while resists indicated it was CC'd. Bards mez usually lasts 4 pulses, it is the reason why they can mez 4 mobs. These partial CC resists were breaking before 1 full pulse almost every time.
With my enchanter, it was essentially the same thing. Dealing with hate mobs, you just had no idea when something was going to break and start raping people. CC is so unpredictable that <any> add was a wipe.
This probably won't seem like a big deal for a few weeks, but once people start getting into their 20s, there's going to be an uproar. The current system has completely fucked PvE crowd control.
I agree with everything you said