I wasn't paying attention to anything before G4.5 unfortunately but here in NZ shops have been closed or restricted since around the movie came out due to lockdown, I went into the mall two weeks ago and I saw quite a lot of leftover G4.5 stuff like a dozen Twilight smashin fashions (none of Sunset Shimmer or Dash, oddly, and the other sets didn't make it here) and the large budget styling G4.5 brushables mixed in with the rainbow reveal Sunny and the big movie friends and the posable crystal adventure sets.
I haven't seen any signifcant leftovers of G4 things so maybe the shelves were cleared to make room for G5 but at Farmers they had a Rarity and Capper Dapperpaws set just sitting there for ages at the bottom shelf as well as the weird Sia pony set but that's it, so I don't really know if that's just what was left of what sold, or?
I went to Toyworld two weeks ago to see if they had anything on special and found they had a boatload of the G4.5 dress-up brushables they must've been trying to clear because they were all 50% off and some more specific G5 things like the favourites together set.
So, don't actually know how well G5 is selling but places carrying G4.5 are seemingly struggling to get rid of them which is a little sad because they're nice toys, I think. The Christmas rush might change things