Based on how good the Hags in JP are, Cover is stalling the coveted and prestigious EN Hag line because the west wouldn't be able to handle the sheer power that is premium hagdom. Someone like Nina from Niji is pretty good but it also strikes me as being like a mommy act. Maybe it's just me but it truly feels played up. Not that it's a bad thing but it's notable to me.
However you can't release some natural hag streamers like Botan, Mio, Korone, Lui, or Marine into the western vtuber sphere without full proper preperation. The weak would cry out and vanish into dust within moments.
Honestly though, I really wonder what they would end up with if they finally release one or two of them. Covers selection for talents have generally been shown to be consistently solid over time. Peoeple slept on Lui and Kaela for a good couple months before people noticed them.