Tbf I said maybe and I meant without multiscale lol. Same for gen 9
Nah, you can,t Ban Multiscale, since Nite has never been any close to broken. If Lugia its unbanned, it has to be unbanned entirely.
Obviously in Gen 5 it would be way too broken. It has Toxic, 16 PPs Roost and Knock Off still has low power. It wouldnt even check that well the controversial BW Mons, while easily dominating the rest of the meta.
In Gen 9, things are less clear. Lugia now has no Toxic, just 8 recovery PPs and a terrible typing exploited by Knock Off, which half of the meta has. Now, the last part is solved/mitigated by Tera, but it does mean that Lugia will be the Tera user in 80% of the battles, just like Garganacl is. On top of it, Boots will be needed 90% of the time (though I can see Specs and Grassy Seed Lugia being viable). CM sets will be solid and quite dangerous, but there is no combination of 2 moves that covers the whole meta and the +0 (and even +1) power is lacking. Non ironically I think that not using Stabs and instead opting by Boltbeam (+ Tera Electric, Steel or Poison) is the optimal play, since it will give Lugia a shot of breaking or forcing Tera vs Unaware users. I still think that most teams from any style can easily handle Lugia.
Now, is Lugia good vs the broken Mons of OU?
Vs Gambit: needs Earth Power, offensive EVs and Tera to win, otherwise Gambit can boost and win.
Vs Gholdengo: better, CM + Tera should win. Scarf Gholdengo with Trick screws Lugia though.
Vs Waterpon: Stab Aeroblast, this is a good contribution of Lugia to the meta.
Vs Gliscor: Fucked by Toxic but with Tera + CM wins vs all sets.
Vs Raging Bolt: Needs Tera, but wins with it.
Vs Kyurem: Same, though can be screwed by freeze (doesn't win fast enough) or DD sets.
Overall I am not sure if Lugia presence would be positive in OU, but I do think it wont be broken, even with Tera. Much better Mon to test than Palafin for sure.
Still, currently I wouldnt test it, Gliscor is current target, and regardless of the outcome there, I would go after Waterpon or Raging Bolt after the suspect, then Kyurem again, and only then think about some retest, of which Lugia, Archaludon or Zamazenta Crowned would be the most desirable Mons.