Hancock can hold her own against him and dude Kat’s CoA range is not that good. Again Flambe was able to interfere in his fight without him noticing. You can’t use the ceaser excuse
We legit saw how FS wasn't that helpful against things you can't see with Luffy and Apoo. Also, if Katakuri can't keep track of more than one person because of Flampe example, then he shouldn't have been able to dominate the Vinsmoke siblings, should he? He was not paying attention to his own underlings lurking behind the walls. That's not the same as fighting multiple opponents at the same time.
We already saw him outmaneuver Jinbe, Pedro, and Bage casually as a matter of fact. Also, Flampe's needles are called silent needles, so they're some harder objects to sense. Ain't nothing silent or undetectable about Kuja arrows. I already said Hancock is the only threat to Katakuri, which means she can hold her own against him. It's her underlings that you're overrating.