Rodri is way faster than Busquets though I'd never call him fast and also way more agile though again he's not exactly Kante agile. They are very similar players but Busquets is far better on the ball but far worse at actually defending. Rodri is probably the best dm in the premier league in the tackle and rarely if ever gets beaten. In fact he probably gets beaten less than Fernandinho did which is why we don't tactical foul as often.
He really struggled with getting to grips with the physicality of the premier league for well over a year but now he's found his place and is up to speed. Like funny enough Fabinho both were written off as flops after 1 season and I'd argue it took Rodri longer to adapt. Honestly I can't say who's the better player, Fabinho is more physical but I'd say Rodri is the better passer (although Fabinho is pretty good), better in the tackle and in the air. I honestly couldn't pick one over the other, I do think Rodri would really struggle with Klopps system though and Fabinho wouldn't struggle quite as much at City.