I think the odds will adjust back some before the season starts, but currently reflect the simple fact that Irving was the best player in the trade and there is a lot of uncertainty regarding Thomas' hip, which became far more publicized and discussed after the trade. The Cavs will enter the season as the favorites, but the trade definitely closed the gap for the simple fact that Irving is just flat out a better player than Thomas and a guy like Crowder is a nice player to have he is a bench role player and they don't move the needle in these types of things (and Zizic certainly doesn't move the needle at all for the Cavs' odds). If both teams enter the playoffs healthy (or at least mostly healthy), I think most people would rather have James, Thomas, and Love then Hayward, Irving, and Horford. I think Cleveland also has more quality from 4-12 as well, at least this year. I don't even think Zizic is on the 12 man active roster for the Cavs while he was likely a rotation level player on the Celtics. Going forward obviously Brown and Tatum are far more valuable than any non-big 3 player on the Cavs, I just don't expect much from them this year in the way of real contribution to a contending team.
And for the record, I'm happy that Boston now has the 2nd and 3rd best player in the series, I just think the gap between James and Irving is immense which makes up for the smaller gap between Thomas and Hayward at 3/4 and Love isn't that far behind either ahead of Horford (though Horford is the better defender still). The role players are all just role players but I'd take Thompson and Crowder over Smart and whomever else you want to add without thinking about it. I think Rose still has some life left in his legs and is a tier above all but Smart on the C's (outside of the big 3). Now maybe Brown comes out vastly improved or Tatum really impresses from the get go, and that all changes, but as of now, the Cavs will be favored in a playoff series against the Celtics as the teams are currently constructed and with the assumption that the teams are generally healthy (or at least the key players from each team).