Domi-Reversi is an over-used plot device that didn't work on the god fruits for whatever reason hence why Imu decided to descend himself. The moment that happened it has always been very unlikely we ever see it again. Moreover why would Imu go out of his way to use Domi-Reversi when he's already here. Not to mention that we've already found a solution for it via chopper.
So it is really a plot hole, it is just story progression imo.
Cause adding to your forces is always a good idea? And adding someone who imu literally acknowledged as strong. It would also be very effective psychologically against the shp and elfabians.
Out of his way? He domi'd Rocks and the giant captains in seconds lol. There's literally no reason to not use it. It isn't difficult to pull off as far as we've seen, and doesn't have the problem of damage reflecting back to imu if the domi's are defeated unlike knight pacts do either.
Imu doesn't know whatever choppa did iirc. And i doubt choppa could tag a buffed gaben so easily.
Imu is also on a timer here. He's actively being damaged by being in the lower realms. I think in the first chapter he arrived, he even mentions being in a hurry or something.
Taking all that into account, turning Gaben after he cut off his hand would have been an extremely effective play from imu. The only reason he didn't do it, unless we get some new info about why it wouldn't work on gaben, is because the good guys would just lose.
ie, PIS. Plot Induced Stupidity. Where characters overlook or outright ignore great decisions because plot needs them to not do that.
It's a plot hole unless something changes.