I don't think 3 casts is the right metric to weigh it against. Do we expect that of any other creature?
I've had ruinator played in my cube in a UW tempo deck that otherwise had little to specifically do with the GY, and it ran perfectly fine. If I remember they got two casts off it in one of the games against me.
Add in any GY shenanigans (which my cube has a lot of), and it can rumble in lots of deck easily; and yeah the 3 CMC reanimate/search/etc cards are real fun with it.
I've had ruinator played in my cube in a UW tempo deck that otherwise had little to specifically do with the GY, and it ran perfectly fine. If I remember they got two casts off it in one of the games against me.
Add in any GY shenanigans (which my cube has a lot of), and it can rumble in lots of deck easily; and yeah the 3 CMC reanimate/search/etc cards are real fun with it.