The difference is that Gaga and Katy had never released at the same time before the Roar vs Applause and Prism vs ARTPOP mess. However, Rihanna and Taylor have released at the same time twice before, with Speak Now and Loud, and Red and Unapologetic, and obviously no one destroyed the other.
This is true ... Although Rih her singles tend to outshine Taylor, while Taylor has a better US album sale
If Bey would actually do some promo this era could've been a beast but so far it's just an average era.
She's not doing bad, not at all, but it could've done a lot more.