Maining a champion doesn't mean you play them a lot. They could honestly be your least played champion at times. What it means to main a champion is that your chosen champion is fun to play and never gets old.
I've mained Garen since I first played him in Season 1. I go back and forth between playing Viktor, Sejuani, Taric, and other champions that I really do enjoy, but if I keep playing them I will eventually get bored and move on to someone else.
Garen, however, I have never gotten tired of. I've gotten tired of top lane, and so I occasionally play Garen mid or support, but I've never been tired of playing Garen.
When I have the time to play a lot I'll go on sprees where I play mages or true tanks or even "try" to learn ADC where I never touch my main, but I always come back. There's never a time where I have the chance to play Garen and I don't want to. I may want to play someone else more, and so I don't pick Garen, but that's not the same as actively not wanting to play him.
So here is the question for you: is there ever a time where you are bored of playing Shaco? If the answer is no, then you don't technically main him.