I had to give it a try to be sure, but I don't know what you mean. Keeping all you enemies stunned for something like 11 turns and at the same time maintaining +30 defence and +30 saves for 5 turns... OP you say?
To be fair, PMs are ridiculously OP anyway. This seems to be about par for the course. They are the only class where I have been able to stand in the door of the Giant stronghold and lay waste to everything without even moving. Still, I found this trick to be quite cool. A lot of people have had the opinion that Spin Fate is a bit useless and wondered what the point was. At first I thought that Seal Fate only acted on one target. But it acts on *all* the targets you hit. Not only that, but it bumps up your Spin on every hit.
I was finding that against a tough boss (found one in a chest), Stun -> Seal Fate -> Damage and then when Seal Fate runs out, Time Skip. By the time Time Skip is finished you can basically do it all over again, so you are right about permanent stunning.
On balance, though, many bosses in the end game are pretty stun resistant, so trying to get that first stun in might be quite difficult. PM doesn't have a lot of other debuff options (I suppose spatial tether should also work???), so maybe not so OP for end game...