Is Olo better than SPC?

Olo has mag regen and minor aegis as its 2 to 4 PC bonus. Spc has max mag and spell damage as its 2 to 4. For most 4 man content the max mag and SD is superior to mag regen and minor aegis as it increases your damage output. In a good run my templar healer hits 30k dps running spc, less in olo. In 4 man that counts. In 12 man it's less valuable.

Is SPC a good combo for Dungeons?

SPC is best in slot, and so is RO+JO, but only if worn in that combination, and only in trials. For dungeons SPC + MA is BiS, and you could argue that SPC + PA is BiS if your tank isn’t using that. I remember SPC + JO being BiS, before RO existed. Also, for a while Olo overtook SPC, but then it went back to SPC.

Is olorime better than SPC?

SPC works better for chaotic, uncoordinated, inexperienced groups that run around (instead of through) ground based heals needed for olorime. Ideally you want SPC 5-piece always active, whereas olorime is perfect for one-barring, giving a lot of control about when to fire it off. It's like they are both good?!?