Apparently the trigger for Barry's level increase is different from Dawn's/Lucas's? I assumed that both roster boosts would happen after entering the Hall of Fame ten times (like Barry in Platinum) but only Dawn had her higher-levelled team when I battled them both today.
It's especially sad because it's basically impossible to beat the hyperbuffed E4 that many times without ending up with a full team at level 100 or like 10 level 90+ mons, so even the 10-level boost wouldn't help him that much., but without it poor Barry is getting left behind by Cynthia, the E4, his dad, all the Gym Leaders, and now even Dawn lmao.
EDIT: also this is a total sidenote but AI trainers still don't know how to assess the effective power of multi-hit moves. There are several trainers' Mamoswine you can battle that know both Icicle Spear and Ice Shard but they always seem to see Ice Shard as the stronger option. Honestly it's saved my butt a couple of times in the Battle Tower.