After I restarted my run recently, I would like help on my team, (currently on whirl islands)
Blaziken 55 Chesnaught 55 Greninja 52 Venusaur 47 Gardevoir 52 BLANK SPOT
Just based on typing: You are weak to Flying, Poison, Psychic, Fairy, Fire and Ice.
Almost all can be adressed by adding a steal type pkmn, so maybe Metagross, Excadrill, Bisharp Empoleon or Aegislash might fit.
You’ve got a pretty good team going. Just survive with those 5 until you can get Heatran (available next content patch), who is the best offensive and defensive complement to your lineup.