Watching that Cavs-Warriors finals game today on NBA network, you could see how LeBron tends to dominate the ball with his one on one play. I don't think Irving cared for that. He wasn't getting much opportunity 2nd half.
They'll be more ball sharing in Boston, and Irving will be central to that as a PG. He'll score plenty, but I think he will be called to distribute as well.
Stevens has a very big challenge here, with almost a new team expected to improve over last year. They will have to come together very quickly.
Right now, I don't see the Cavs and Celtics as that much apart after this deal. Assuming IT gets back to normal play. I also think the deal increases the chances of Lebron staying in Cleveland. The Cavs have added depth, and have a high lottery pick to look forward to next year.