It's not so much about having 10 SSRs but having 10 weapons in general. If you've been playing from launch and getting everything important from events, I'd say you should be pass the point where any extra SR weapons you get from events is becoming a waste of space that can just be used as skill enhancement. The only SR weapons that I already have leveled that I'd ever bother to replace with other SR weapons are arcane weapons, since they're incredibly weak, anything else just feels like a waste of resources, especially if they're already maxed out.
For souls, as long as you have something for Mordred, Joan and maybe Andromeda, you're pretty much set as they're honestly the only worth using souls in most scenarios.