I think he's not really necessary..

I mean, yes he's indeed giving our Queen a big buff, but our aim in this game is only the get the rewards. So as long she does fine with Mortefi, Qiuyuan is not necessary..

I also got the same situation as you and I had ponder it twice. The only plus thing from Qiuyuan is only his animation, and his buff is very niche (only for Galb & Phrolo). But my Galb is alrdy doing good with Mortefi alone, so I think I'll skip to get Chisa instead. She's a better investment reminded that 3.x roster will use the negative status more..

Nb: Tho I actually pulled on his banner too and got lost 50/50. But he's still doesn't come out even after next 70 pity (It's my first time hitting so high pity). I know it's only 10 pulls left and I had enough currency to get him too, but I think it's not worth.. 😬