Are Arbiter's phantoms OP?

I am not a terribly strong Halo Wars 2 player, but even so, I’ve found that, once Phantoms get going, they seem to be almost impossible to stop. I’ve held off people who had control of the entire map for an excessive amount of time, leaving me with a paltry 1 or 2 bases before finally pushing and ultimately winning the game. Has anyone else found Phantoms to be a bit… overpowered? Or is this just a thing that drops off after you get past diamond rank?

All I do is shove as many Enforcers, Hunters, and rangers into them and upgrade infantry first so that when they finally explode the infantry have more than a sliver of health