I could've picket any mon but copperajah and duraludon won me a lot of battles due to team synergy, in fact I won one 1-3 with duraludon and copperajah also fills in that role. Just because a pokemon isn't viable doesn't mean you can't use it - I remember a person getting top 3 of an regionals using yanmega - with no competitive usage for more than 6ish years. Duraludons physical bulk lets it live attacks, disrupt with dragon tail and follow me clefable prevents and fighting type attacks with it! I got a 1320 elo using duraludon - but lost it all when I thought my cat team was viable. (my elo WAS NOT 1320 before!), so I have a lot of experience with duraludon and not much with copperajah, so I don't know much about it, all I want to say is say is despite the normal people who decide whats viable, theres always a yanmega.