Personally, I don't think the Mavs went from really good to mediocre at the very point Kidd became a Mav, although the record of 16-13 after the trade would indicate otherwise. Now hear a beloved Mav fan out, I simply think we became victims of poor luck and the timing caused people to connect it to Kidd.
Poor luck you say? Well our beloved Dirk missed 5 games (1 suspension, 4 injury) and we went 2-3. Let's assume Dirk playing would've turned one of those losses into wins (17-12)
Then, we went 1-7 in games that went down to the final minute... . Some may attribute this to a lack of coaching, execution, whatever... but I attribute it to fluky bull (in any case, I certainly wouldn't attribute it to Kidd). A weird bounce, a fluke shot, a turnover etc etc... some of these things are completely random in games decided in final minute... so let's adjust 1-7 to 4-4
... (20-9)
So, although we went 16-13 after the Kidd trade last year, I don't think we played as bad as our record would indicate. 7 of those losses were in the final minute (3x LA, 1x SEA, 1x PORT, 1x SAS, 1x BOS), 3 were without Dirk (1x GS 1x DEN 1x HOU), 1 was v the Spurs when our beloved Dirk went out for the final 15 minutes, 1 was v the Hornets when Kidd had only practiced once with the team, and 1 was to the Jazz legitimately Our margin of victory in games Dirk played was +7.8, which would be right there with Orlando right now if it was this year, and +5.8 overall which would still be 5th in the league right now.
Of course, that all went to in the playoffs, but still... we've had perimeter problems for years and Devin, Kidd, Jesus Christ, it doesn't matter who is the PG when our 2nd offensive option is shooting 28%.
Now this year it's different, Kidd's production is more or less the same but the margin is only +1.6, defense has regressed badly and part of me thinks we miss Stackhouse, inefficient as he was a guy who could come off the bench and give 8-10 points.
Well, our beloved Mavs are mediocre now, but in the 2nd half of last year, I thought we were good. It wasn't just an instant transition IMO.