I don't believe he would have set himself up for an uphill battle. Unlike Roxanne who seemed to have stood in the same spot attacking haphazardly around her, Isley isn't going to sit by and let Cassy flutter about the battlefield. He will pursue her. I'm sure he is close to her speed if he is faster than Rigardo. Isley's form isn't built for keep away, it's built for adapting, which is what he will do.
Isley was an all-rounder in terms of fighting. He has range, and close combat techniques. He states in the fight vs Priscilla that normally he would wait for the opponent to strike first. This shows he's conservative, and strategic. However, an all-rounder does not necessarily have the advantage against Cassandra. Her ability is pretty all-round in more ways than one. But, it is very specialized at the same time. If he wants to wait around to see the first move, then he has probably lost due to the unpredictability of it. He would be setting himself up for an uphill battle after letting her set the pace. If he were to go on the offensive first, then he is setting himself up for a fatal counter. From what we've seen, he has no real keep away moves like Roxanne had.
Isley will most likely not use his shield. He will probably still to dodging as one shield isn't going to do much against an opponent like this. He will probably try to keep his distance and when push comes to shove, he will use his Claymore sword to decapitate a bunch of heads. However, this is risky as the closer her is to Cassandra, the more likely he will lose a limb. Again, I believe this will end with both fighters near death as they both have no real advantage over the other.
Looking at the battle between Roxanne and Cass, Rox seems to be Speed and offense. Cass on the other hand, is speed and Defense IMO. Cassie's style is designed to counter an arsenal of offensive moves. Besides a shield, Isley doesn't show much defensive ability. And who knows if that shield couldn't be shredded by the Dust Eater.