[Corvina]

Yeah, her a-nation time slot was pretty much always the same, even at her peak. She's performing when it's still daylight, but always as one from the last.
And even if Ayu would be much worse than Kuu right now for sales and popularity, I think she would still be performing after Kuu at a-nation - just because of her status at avex.
It just changed in recent years, that the a-nation dates got different headliners, meaning different artists as last act.
But Kuu got her own a-nation date instead this year. Which is totally new and something special. So nobody should worry or make a fuss about it.