You don't counter FS. FS is not something that has to be countered Ndule. You rather need to " break through " its proficiency by still overcoming the opponent due raw combat speed.
Tunder Bagua is one of the fastest, if not the fastest known attack. Base Luffy could partially dodge it due to predicting it with FS. Katakuri's base speed >> base Luffy's and above that, he has shape shifting for even more efficient dodging.
Sure, with enough speed you might catch Katakuri sometimes, but
1) King is not near that speed
2) Katakuri has a second mechanism for protection (super hard Haki defense)
3) He can take a lot of damage (several blows from G4 and fighting with a part of his torso ripped out)