What could possibly make you say this?
Take the GGG fight out of the equation completely and Brook was already considered a hard fight for anyone in the division, let alone someone as unproven on the world stage as Spence.
I really don't know how anyone could look at both styles and think Spence will whoop Brook, i'd be interested to see a breakdown on that. I like the look of Spence, but he's best win so far is Algieri, who is a complete none puncher, there's many more question marks over him in this fight than there is for Brook.
Stylistically, I like the fight for Kell more, he's excellent against southpaws and carriers serious power for a WW. Great jab, great timing, and snappy speed for a welter. Spence gets hit a lot, I look forward to seeing how he deals with the power.
his fight will likely go to a close decision, or a Brook stoppage if it turns out Spence is chinny. I don't see Spence blowing Brook out of there, it will be a pure boxing fight for the most, and no one at welter is outclassing Brook in that kind of fight.