If their big 3 in Cleveland are healthy, the only way they don't ever win at least one championship is if the Thunder get a new good coach, or the Bulls have a healthy MVP level Derrek Rose and DPOY Noah for the next 4-5 years.
I think this season, Chicago should be a monstrous team if they can stay healthy.
Rose, Noah, Gasol, Butler, McDermott with Taj and Mirotic off the bench (among others).
Other than that in the East, perhaps Hibbert steps up a level and George comes
back an even better player but it's unlikely. I think the Bulls and then the Wizards pose the biggest threat to the Cavs. Wizards should be slightly better than the Heat.
They'll be better on defense than you think, because Lebron will force them to be good defensively- he'll make sure everyone plays hard defense or he'll get rid of them.
They can get defensive role players and specialists easily, or they can go after someone like DeAndre Jordan or Hibbert as a free agent if they feel Irving is under achieving.