Yes, there’s a lot of potential in both. But for HSTR, as I understand Nihilus, damaging him with basic attacks fuels him. So having BB8 call another character to use another basic attack actually will just apply defense down on two characters/cause Nihilus to regain more protection. Whereas R2’s CA cleanses those defense downs, preventing Nihilus from regaining protection and reducing his annihilate cooldown when he uses force drain on debuffed characters.
Basically the train of thought is: more attacks with BB8’s RWTP vs. less protection recovery with R2’s CA. It’s pure speculation which one would lead to a higher overall score than the other.