Just as mentioned before, there are many ways to utilize time.
Besides affecting enemies, it can also affect oneself.
Fang Zheng didn't care about Emiya Kiritsugu's low-level Inherent Time Control; it was merely speeding up or slowing down his own body. To put it plainly, that method was only necessary for mortals like Kiritsugu to rely on in combat. For Fang Zheng, his speed, comparable to that of a Jumping Bug, was sufficient to pin Kiritsugu, even with ten times the Inherent Time Control enhancement, to the ground and beat him a hundred times.
Of course, whether Fang Zheng would die with a body modified by the Zerg was still a question, but whether Emiya Kiritsugu could survive was definitely not.
So, for Fang Zheng, there was only one other method of manipulating time that could allow him to benefit while weakening the enemy.
Future Sight.
