I don't really agree with Soren's viewpoint either. You play the game any way you want really. I have levelled non-meta characters in plenty of games before, because I enjoyed using them. I never shoot for the top in mobile games, because I could never match the Whales spending power and the stress of trying to be at the top isn;t worth it for me. yet others strive on the stress, even if they are doomed to not hit the top spot. Would never call them out for playing the game the wrong way or anything, it's all personal choice.
Plus, with the special quests like needing to have certain teams (like Swords, Lances etc) then I think most characters will have a use at some point.