White_Donkey
Garp in his prime casually destroyed 8 mountains to train for a fight against Don Chinjao using just his armament haki and physical body strength If Ace trains his body and armament haki to a high degree, he will become the immovable object. Adding unto that the abilities and speed of the glint glint devil fruit and Ace will be an unstoppable, impenetrable, light-speed tank. Capable of destroying anything and everything from any range within sight. With no one having Haki of any kind and spells/magic probably requireing some preparation time, even if just a few seconds, everyone is screwed. Armament haki being not so useful in this world as in the one piece world my *ss.
No. Predicting where the attack will be directed doesn't mean you need to be faster than light. Kizarus can't redirect his attacks at the speed of light because he has a human brain. He still needs to think, "ok i gotta aim my beam right here", and Luffy would respond according to the intent Kizaru projected using Kenbunshoku Haki precognitive abilities, so the way I see kizaru can move at the speed of light only 'transforming in light particles' and when he attacks he has to be in 'human form' (but light-based attacks are still light speed example: light beam) just imagine Obito kamui