Without Isabella the Destroyer, Jiang Fei would lose 90% of his combat power. If he were to lose Ariel as well, that would be 99.99% instead. That was how weak Jiang Fei was in the face of Level 5 fighters.
Although the martial artists were afraid of Zhuge Shanzhen, the Unknowns were not. They might already know that Zhuge Shanzhen was nothing but a fictional character created by Jiang Fei himself. If Isabella was removed from the picture, Jiang Fei would be looking at a complete and utter defeat. When they resurfaced again, it might not be a confrontation but a full-on attack.