To the OP, in response to your points.
1. We overcame the Bulls largely due to a series-ending injury to Rajon Rondo (who had been killing us in that series) in addition to the elite defensive job Avery Bradley did on Jimmy Butler - Bradley is now gone.
2. We barely overcame the Wizards in a 7 game series because the team played with no heart and no energy in half of those games. They basically laid down and said "do what you want with me, I won't fight it". There was a lack of effort on both ends of the court in the games we lost - and the blowout margins were proof of that.
3. We got destroyed by the Cavs because of terrible rebounding (which has gotten worse this year) and because, as with the Washington series, we played with no heart and no effort to start the series. When IT went down the team seemed to play motivated again (as if they wanted to play harder for him, or were making up for the loss) and after actually playing with some effort and heart for the first time in the series, Boston actually took a game.
4. The Cavs do have a poor defence, you are right. But they also had Kyrie Irving (one of the best closers in the game) and Lebron James (the best player in the game), and the duo of Kevin Love and Tristan Thompson (one of the best rebounding frontcourts in the NBA). When you have three offensive superstars on your team who are capable of scoring 70 PPG on their own, combined with two three frontcourt players who are capable of pulling down around 30 RPG between them, then you can kinda make up for a lack of great defence.
Unfortunately our top 3 scorers only averaged 60 PPG last year between them, our top 3 rebounding starters only averaged around 17 RPG between them, and our bench is made up almost entirely of young prospects - many of whom have yet to play a single NBA game. So we cannot get by with a bad defence quite so easily as Cleveland could last year.
5. You take a Kyrie three over Steph in the finals over any AB defence? That's interesting, because without AB's defense against Jimmy Butler in Chicago we probably wouldn't make it out of the first round, I which case your Kyrie 3PT in the finals becomes nothing but a pipe dream.
6. Our defense is not better then last year, don't make me laugh. Our top six defenders last year were (not in any order) Avery Bradley, Jae Crowder, Al Horford, Marcus Smart, Amir Johnson, Kelly Olynyk. We lost four of those six guys. In return we gained two above average defenders (Morris and Baynes), one average defender (Hayward) and one terrible defender (Kyrie). The only consolation here is that Kyrie replaces Thomas, who was an even worse defender. Other then that we are worse on defence - way worse. Unless Brown and Tatum shock us that is.