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I think it's important to have a balance between being a Smogonfag and a Karenfag. Use the pokemon you like, but remember that the ones that are seen in most copy-paste teams are there for a good reason; They work well even if you suck.
That doesn't mean that you have to give up on your favourites to get gud, it just means that if you want to use your bro you need to think outside the box a bit. Come up with some clever tactic that makes your bro viable, and mop the floor with OU: The Team.
In short, use what you like, and have fun. Just because someone else likes Arceus doesn't mean that you'll never beat them, you just have to think a bit.