Regidrago auto loss to Archaludon?

My son (seniors division) is newish to the competitive scene but has placed well in the last 2 US regionals we attended. He plays Regidrago and is looking forward to playing it again in San Antonio. However, he is having a really difficult time against Archaludon EX with Dialga. We’ve been testing a few techs like Kieran or Defiance band but that only feels marginally better. Would love some advice against this matchup. Thanks!