Bruh...
It almost looks like SIU had no idea of what to do to make those two destroy the portal and came up with this amazing idea at the last minute. Not that I'm complaining, it looks so ridiculous that I actually like it lol.
Watch how it actually works and Perseus' pessimistic ideas end up coming true. Actually, I wouldn't mind it. I prefer the portal getting destroyed and the FH not coming yet than to see the FH coming now and completely overshadow all the interesting plot lines we have. Considering what we had with Whitegarment, the warping should be very fast. It's not like we have zero evidence of them being capable of warping to different places by themselves either. We have Death Lady saying that the Great Warriors can enter Karaka's dimension on their own. Urek also used a technique called Spatial Distortion to warp where Gustang was (although it was on the same Floor).
We'll see. Perhaps the portal is not destroyed and SIU goes back in time a bit and manages to end most of the interesting plotlines before the FH comes through the Gate. That could also be another possibility, because if he appears right now, it's gonna be overkill IMO.