When You don't normally use a champ but your're better than someone who mains them

maybe you're just playing at a shit elo

You say "Main" as though that means something. People who "main" champs only matter when they are actually good. There is a big difference between a bronze "main" and a Diamond Main. The former simply plays that champion a lot, while the ladder being someone who actually understands the champ.

At my level I'm probably better than most people who "main" a champ at anything under gold. Having a basic understanding of the game will let you be better than most people.

Depends on what elo you're in and what champ they're playing.

In lower elos it's kind of obvious, and sometimes even good team-reliant champ mains can't do shit when their teammates are kind of stupid. (RIP support mains)