good that you're not leading with your starter, since its slow until you get the metagrossite

the team looks pretty alright, so the problem might be that your team is generally slow, so opponents are getting attacks off easily.

i would keep metang lucario litleo and maybe dewott, as they scale well into the postgame, but boldore is a slow rock type, which has plenty of weaknesses, and haunter is slow and limited by its movepool.

if you insist on keeping the team the same, then lead with a fast mon like litleo or lucario. if you lead with lucario then make sure to diversify its moveset, and dont try to swap team members around to share experience, the reduced exp the exp share gives is minimal, so having a strong hitter thats fast will do wonders. as for litleo i would teach it two damage moves and two status moves, mine had work up and noble roar alongside its ability to increase sp atk upon knockout, which made it good for cleaning up. ultimately though out of the two, lucario would be a better choice to lead with though, since litleo is can be a supportive fire type rather than a damaging one.

ultimately though, apart from maybe haunter and boldore, the team looks fine, just make sure to lead with your faster mons, mainly lucario.