they're about on par for Mythic creatures of rank 8 in terms of abilities.

I do not consider this a meaningful statement, as creatures of MR 8 are of basically random difficulty.

Julunggali is a big snake with a couple of attacks and some SLAs, Devastator and Iron Colossus are similar but big robots. No true seeing, no ability to move + attack, no ranged attacks except a couple of weak ballistas on the colossus. They are essentially jokes for their CR, let alone CR + MR, they are basically shut off by invisibility or any sort of planning. Devastator is the only one with an escape hatch (plane shift) if things go against them.

Meanwhile a Solar Pitri is super dangerous, packing three escape hatches, four irresistible disintegration rays, powerful SLAs like mythic wish and miracle, and the ability to come back if killed by a non-mythic source.

These creatures are on a complete tangent from that scheme, given that they are swarms and their multiply ability. Within 1 day they have 1,440 copies, so the GM needs to tell you which is the ur-swarm somehow or you can't do much. They are more like a spell effect or puzzle rather than an actual creature, and really aren't "on par" with other MR 8. It is more like the other MR 8s are playing chess, some are good some are bad, while these are playing the MIT mystery hunt or something.