It's really a question of what part of the game you want to prioritize. Resistance can make a lot of parts of the game a lot easier, but they aren't that great in arena right now. Han can help in those areas too (he is also very good in TB, and he can make GW easier with the guaranteed stun of anybody you want in each round) but he is not a team unto himself. He is good in arena, but the benefit you will see won't necessarily be as big since your current team is already pretty strong. If you are struggling with TB and GW, then you might see a larger return from Finn right now.