Direct statement like that needs to be taken with huge grain of salt
I was about to answer Geo post but I can do it here
Obviously Ray can sense haki, can gauge how strong someone haki is, likely knows BB past and what he did (Ace, MF, WB pirates etc etc)
So yeah Ray can totally sense that BB is indeed a Yonko in name and power
But obviously he can’t sense BB smarts, his trickery, the destructive power of the Gura, the weird and powerful power of the Yami, BB own weird body etc etc
I don’t say that Ray had no chance to beat Current BB but to say Ray statement means at 100% in Prime he was above current BB is not true for me.
Ray was at a level where it can be true but not certain. Especially with a guy like BB.