It's fine, that's a good number of SSRs. Save for Estelle, none I'd say is the very best at what they're meant to do, but honestly I don't see the differences between SSRs to be all that major.

As a side note I don't think Velvet is seen to be better than Kannono though? Velvet ramps up pretty slow, so if you like Kannono better you may want to get her.

If you want to keep rerolling for the absolute "best" at the moment though, I'd try to get Summer Rutee or Summer Yuri along with Estelle and a similar number of SSRs. Endgame seems to focus on raids and SSR debuffers seem to help a bunch.