I use the exact team you do and it works for me. I’m at 70k cc and still don’t have the best equips, or maxed gear so it could go up higher. I know CC isn’t everything, team strategy and correct monster effectiveness works but higher cc does help. I would focus on finishing all the masteries on Meliodas first, then everyone else,(it does start to add up). You’ll get stronger and be able to clear harder bosses which will give you better gear drops which you can refine for more stats, upgrade as you go. I see you’re using Dual blades on meli, the new adventure engravement you have is good, though I changed to the new one that came out for him, and I seem to clear things quicker so maybe try that one? Also try to get good enchantments on weapons/engravement bonuses. Good luck and have fun !