I think it's really too soon to tell, to be honest.
On one hand, on paper, the addition of Crowder makes Clevleand much stronger right now. He is the tough defensive wing they have needed for years, and he also gives them an extra shooter and efficient support scorer on the offensive end. The combination of Crowder/Lebron can now match up pretty darn well against Klay/Durant - while Love on paper is a solid match for Draymond Green.
On the other hand, in the real world, Cleveland might have gotten less competitive when it counts. Bringing in Thomas defensively gives Clevleand an immediate Achilles heel that they never really had before, which can be constantly exploited by opposing teams. Teams will take advantage of size mismatches constantly, and that will force Clevleands other wings (Crowder and Lebron) to help out. Lebron tends to be pretty lazy and takes more then his share of plays off on defence, so I can't imagine him running around helping on Thomas every time there is an exploit...meaning there is going to be a LOT of pressure on Crowder to make up for all of Thomas' defensive problems. In Boston Bradley and Crowder as a duo were able to take turns covering and helping out with that mismatch, but now it's all on Crowder - how will that impact his ability to defend his own man?
Secondly, Cleveland just lost (arguably) their best clutch scorer in Kyrie. It was usually Irving (not Lebron) making those big game winners at the end of games. As good as they are on paper, Kevin Love and Jae Crowder have both shown a tendency to shrink in the biggest moments. Thomas on the other hand has shown that he sometimes struggles to be his usual dominant self when teams are able to crowd him. Will he be able to be that guy, and take over Kyrie's role as the closer?
Will Crowder be able to effectively play the SG spot? Does he have the ball handling skills? Does he have the quickness to defend opposing 2's all game long, and occasionally switch on to 1's when IT is beaten?
IT excelled in Boston as the #1 guy, but has struggled in the past (Phoenix, Sacramento) when he's had to play second fiddle to other guys. Will he be able to excel in Clevleand as Lebron's sidekick? Will he be able to adjust his game and play off the ball now that he's learnt to excel as the primary ball handler and playmaker?
On paper Cleveland seems to get much better, but hard to see exactly how that will translate to reality.
For Boston, there are also many question marks. We get significantly younger, and Kyrie's ages better matches up with Hayward and out prospects - so our window of competitiveness has likely increased significantly. Kyrie and Hayward can form the core of this team for the next 5 years or more.
However with Kyrie, Hayward and Horford likely starting at PG/SF/C - who joins them? I've read that the plan is to start Brown and Morris. I see pros and cons to this ides.
On the plus side, starting Brown means he'll get the minutes he deserves, and a true opportunity to develop. On the downside it means we are putting a LOT of faith in a 21 year old player to step up - a lot of our success will be riding on his ability to step up, and that's a lot of pressure for a young player.
Starting Morris and Horford should give us a frontcourt that is very versatile on both ends of the court, with both guys being able to switch on multiple positions and score inside/out. I also like the personality mix - you have Horford's grounded, calm, veteran presence alongside Morris's aggressive, energetic and physical style. On the downside both of those guys are streaky on offense, and our rebounding with that line-up projects to be even worse then it was last year (with Amir / Horford).
Another questionable part is then bench. Considering we already lost so much depth (Olynyk, Green, Jerebko, Zeller) losing Crowder and moving Brown into the starting 5 leaves us with a very young and unproven bench - it's hard to predict what we will get from them. It could be one of the most dominant benches in the league, or one of the weakest. and that will largely depend on what we get out of Rozier and Tatum.
I expect Rozier to play the full time PG spot off the bench, with Smart alternating between SG/SF and Tatum alternating between SF/PF, and Baynes at Center. We can easily predict what we will get from Smart and Baynes (toughness and grit, which will be great for us) but we don't really know what we will get from Rozier or Tatum. If Rozier can step up and be that guy we've seen flashes of (on a more consistent basis) then he could be a difference maker. If Tatum steps up and plays with ROTY form then he could also be a game changer. If both guys step up, then we could have a truly dominant bench. If Rozier fails to take that step and Tatum struggles with the transition, then out bench could be (offensively) horrendous beyond words.
This move for us clears up playing time for young guys like Rozier, Tatum and Brown - and I think that was necessary. Those guys need reps in order to develop, and they all have tons of potential. But the flip side is that this means we are also putting a lot of pressure (and hope) on the shoulders of three very young guys, and that's a big risk.
I'll say one thing - it should be a very fun team to watch.