Lebron traded TOSB Wade and Alpha Bosh (who hangs out on the perimeter now, which has caused the rest of his offensive game to regress) for a young and explosive point guard in Kyrie Irving and two up-and-coming prospects in Bennett and Wiggins. I'm not convinced he has given up anything right now. The East is still wide open and the Cavs will be in the mix as long as their young players show up.
The question which remains to be seen is whether Cleveland will be able to bring in more talent season after season to satisfy James. Miami had the full package (money, location, and Lebron) to throw at FAs, whereas Cleveland will only have one of those things unless Gilbert suddenly has decided to stop being cheap.