RoP is manageable on fights without a lot of movement. It's the easiest to keep track of because *visually* it's right there. You know when RoP starts to fade because you see it. It's a constant, as long as you are standing in RoP you passively gain it's effects. The problem with RoP is that it's quite small. If any target AoE is lobbed your' way and covers your' RoP you must cast a new one. Usually you must move first (losing damage) then recast RoP (still not doing damage). Generally the best bet is to strafe as little as possible, RoP, or blink then drop a RoP. This ability is annoying to use in dungeons because you are continually casting RoP before every pull.
I can't stress enough what a chore it is to cast Invocation/RoP before every damn trash pull. Its' really draining a lot of fun out of the class for me which is sad as someone who's played a Mage almost exclusively since 2 weeks of Vanilla launch. I clearly enjoy the class *a lot* and have been around for a host of changes. Other classes have active/instant speed cool-down abilities they use during the fight. I was just in a heroic dungeon with a demo warlock who did about 80-90k+ on trash packs we were clearing using his CDS in combat. He didn't have it up for every pack...but he used it in combat.
Obviously you will have to lose damage sometimes with the lvl 90 talents and how much damage you lose depends partially on player skill and RNG. The way they are implemented currently makes playing a mage optimally tedious.
I haven't worked with Incanter's Shield much. Basically I could see it being usable on some fights where there's periodic AoE. There are plenty of dungeon/raid fights where you'll take damage no matter what. Other fights- you should not be taking damage. If you take damage...it's because you stood in it purposely to trigger Incanters or were bad.
Incanter's shield honestly feels like the obvious 'PvP lvl 90 talent'. It's another damage shield for PvP. You must move around continually as a mage in PvP (this has always been the case). No serious PvP mage is going to run RoP. Invocation is another ability that just screams..."PLEASE PUMMEL ME SO I CAN'T BLINK AND DONT GET 25% DAMAGE THX". Like honestly...what mongoloid wouldn't focus interrupt an Invocating Mage? The shield at least has a pretty good chance that it'll break. Mages are often the train target because if you don't train the mage...it will have more free reign to set-up burst and CC.
Invocation could be a lot less frustrating in PvE (for me personally) if the development team had listened to people's QoL complains about Invocation and for that matter the entire Arcane spec. It's a fact that people complained about Invocation's buff visibility on the beta forums, and also the issue of Arcane Charges only to have the WoW development team do nothing.
Basically....the buff indicating that you have Invocation is displayed in the top right hand corner of your' screen. There's no central buff/indicator on your' character like there is for hot-steak and other talents. Nothing changes visually unlike RoP or Incanter's shield. Both of those abilities visually 'fade' before they terminate. I find myself constantly looking between my on use cool-downs for normal abilities...Ie. Frostbomb/Icelance/FFB procs/Pet Freeze/Frozen Orb/Alter time etc...and also trying to watch Invocation's buff which is not centralized with everything else. I will probably end up getting a mod to track invocation or something I can use to move the buff icon.
It'd be nice if the development team listened to players QoL complaints about stuff like this. This isn't even a matter of not liking the concept...or not liking how it feels when you play it. Those are both other separate and valid issues. We couldn't even get a visual indicator change (which they've done for other class abilities). Invocation is a 25% damage spread...I guarantee you if the WoW devs don't roll something out....there will be a mod that tracks Invocation and gives a visual indicator (not off in the corner) as to when it's about to fade
(5-6 second warning). We'll see it in some guild's raid kill video.