It's only 50, actually. 100 would make it worth using.
Collective Unconscious has in the longest case 11 ticks (18s + 15s = 33s) so you have a 550 HP heal. With 100 HP HoT you have 1100HP thats.... Your reason is with the 100 HP to hold the bubble short and have a 500HP. But so the skill does not work.

I know here comes the question: And now Marius how can the tank surivie the 15s while holding the bubble and why is Collective Unconscious so weak now?

First of all you have to be in Diurnal you want to heal not midigate here:

- Aspected Helios + Celestial Opposition (copicat from AH)^^ + Aspected Benefic (in the OGCD) Aspected Benefic = for 15s-12s you have 600HP Heal (the direct Heal from all 3 spells) and 450HP for 4 time (not five because the GCD use from AP and AB^^)
and granting 10% damage reduction. I know its not great stand there but that is how the skill works and its uncool for raiding but that is like the skill works. Hold it or let it
-> Now to the reson why is Collective Unconscious weak:
With the new Celestial Opposition the AST get a new HoT (not creativ but hey a new hot) so Collective Unconscious have to lose the HP from 150. Or you heal much with stading there. The only thing that change is that with the new CO + CI make the same HP like the old CU. Only the people that "snapshot" the bubble lose HPS but thats okay in the thinking to kick of the 10% reduction anyways.
The HPS is the same like it was in SB (in the time you stand and hold the blue fir.... bubble). After that 15s (in the best case) you can heal again.