Nobody should be missing buffs on 1st intermission, or else your raid needs to work on coordinating when to pop the bubbles. Assuming everything has buff, 1st intermission isn't hard to 1 heal. The main problem with 1 healing is the empowered whirls, which you have to have hybrid use their cds. Non-empowered whirls are easy if your raid don't stand in melee range of boss. 1 healing is feasible nowadays if you can skip 2nd intermission's annihilate (either by going in and afking, or having enough dps to push 10% before it, skipping the phase completely) It is a bit harder to get everyone buff on 2nd intermission, and it's a very high risk to actually 1 heal 2nd intermission.
However, with 1 healing, you should have enough dps to push boss into p4 with at most 2 empowered whirl (1 in p2, 1 in p3) I don't think it's worth it if you cant make that dps mark.