To start off, Kyoya's Leone is one of the strongest defensive type Beyblade's in the series. He has several, several defensive amps in the form of wind based attacks that can serve to blow Kenta away before he can hit Leone. These attacks can also send Sagitario into the air, something Kyoya does IC.
This isn't even mentioning that Kyoya is a much more skilled and experienced Blader in comparison to Kenta, so it'll be even harder for Kenta to land a hit on Leone even without defensive amps since Kyoya has a much higher level of skill and experience. I can show evidence of this if necessary, but it should be obvious.
Also, Flash Sagitario has a big weaknesses, in the fact that most of its special moves are sealed. It doesn't have the claws that Flame Sagitario did, so, Kenta can't use Flame Claw, which is something that gets pointed out in the fight against Rago. So while it's raised performance tip allows it to negate a lot of offensive moves, it also leaves him open, especially against someone like Kyoya who doesn't necessarily focus on raw power.