If the PTR went live now, it wouldn't even be a contest between Invocation and Rune of Power. You maintain the exact same damage bonus, but one allows you to move. What's the point of RoP? There currently isn't one. Not only that, we've seen no mention of RoP this PTR, and the blue posts haven't indicated they see a problem.
It's relatively early in the PTR, but we need to see changes that follow what the design objective should have been for RoP and Invocation:
Invocation: Cast and Forget. A safe spell.
Rune of Power: Requires you to stand still, but you should be doing some insane damage if you maintain a high enough uptime.
Rune of Power needs to be instant cast, maybe with a 1 second GCD, and/or last indefinitely. But even with those changes, it still isn't preferable to Invocation because of the same damage bonus. Rune, in all honesty, needs to be a good 17-20% damage bonus. You shouldn't need a 95% uptime to justify picking this talent over Invocation.
And just like the entire L90 tier, Frost and Fire need to be decoupled from its mana bonuses and given simple mana regen bonuses. This way they can exclusively balance the L90 mana bonuses around Arcane, making it a lot easier to tune the knob if necessary.
Thoughts/Comments? Will we see these needed changes?