Rereading:
Is this a supersonic feat for Kenjaku? Or does it mean that Kenjaku is subsonic but he can put all his CE to speed in short intervals, allowing him to move close to PB's speed in short intervals, but only reacting fully after PB moves several meters??
Also this one:
Because now that I think about it, this second interpretation maintains consistency with people being subsonic, as they can probably do this to react to say, bullets, but consistently while fighting h2h they're only ever moving subsonic which is why they get blitzed by someone who's combat speed is way faster into subsonic.
Thinking about it, this might be consistent with examples like Kamo. Maybe this isn't inconsistent panneling, but rather he can temporarily use CE to give himself nigh supersonic speeds, but it took him like several tens of meters to react to Cursed Spirit Naoya to activate it, maintaining him as a subsonic character: