I don't think JJ helps Cleveland that much. Not as a starter. He is too slow to be at the SG position full time. Cleveland are better off with Shumpert starting and JJ in a bench role but I doubt that will happen.
It was their defensive energy led by Thompson and Shumpert that in addition to LeBron carried Cleveland to the Finals. They would well served not to forget that.
Talent is talent. Giving J.R. Smith's role to Joe Johnson, and Mike Miller's offensive role to J.R. Smith, makes that team much deeper and better, in my opinion. They'll still be an elite offensive team with a sprinkling of defensive role players. If they need to shut down teams down the stretch, they could go to a lineup of Thompson / West / Lebron / Shumpert / Delly, while having much stronger offensive options if they needed to play catch up.