HK Harald doesn't really have a sky split but I'd argue he was just as strong as DR Xebec.
In the same vein it's possible that Sanji and or Zoro never get sky splits via clashes in the series and they are most likely going to be beyond Kaido and Linlin EoS. So I wouldn't really split hairs over that tbh but we can disagree on that.
Reason I set the standard as DR Xebec is coz 1.) Imu is capable of creating lackys on that level (i.e DR Xebec, HK Harald) and 2.) I think the ultimate challenge that will be presented to the wings is that CoC barrier that Roger/Garp and Gaban/Shanks had so much difficulty with.
Agree with you though that given the power inflation in the series atm all of the opponents available to the wings feel a bit lucklustre but all of that could change with Domi Reversi to high top tiers (i.e. imagine Domi Reversi Kaido/Linlin or Domi Reversi Admirals) or the Gorosei getting futher buffs from Imu.
He’s capable of creating lackeys on that level but that feels like a bit of a loophole tbh. Guys like Rocks or Harald don’t appear (Harald was specifically noted to be a rare specimen that Gaban thought couldn’t be stopped at all)
I’m not saying it’s an outright no but I’m still iffy on it at this point
Now the good news is they’ll still more than likely get great EOS matchups IF Oda stays the course with Imu being the final villain
The juiced up Gorosei would be adequate challenges. Really even the regular Gorosei might be with how inconsistent Oda can be with the power levels
One day someone looks like a scrub, the next they feel like a god
That’s why I’ll always wait for a character to have a full onscreen fight before I judge them. Kizaru with his light clones (that he never used prior for no real reason) for example made him shoot up my tier list
For all we know the Gorosei have crazy cracked abilities that Oda simply plot restricted in Egghead (we already know Saturn had this with the eye stun thing that he conveniently didn’t use against anyone else)