I'm not saying I agree with that ranking, but Tatis is more likely to stick on the infield (according to most people) and has a terrific/projectable baseball body, and burgeoning power. I would certainly prefer Bo from a fantasy perspective, but the idea is probably that Tatis will have more raw power at his peak while sticking at SS or at least 3B. The other thing working against Bo is that once some scouts say "the swing won't work against advanced pitching," it's a hard label to shake, so even though he's raking now, the prospect sites are hedging. He will need to keep hitting up through AA in order to totally shed that label.