About champions and stuff

So, I was reading an interesting discussion about assassins, and on a smaller scale, melee champions in general.

And I personally agree with it. The meta right now is in favor of ADC's to the point where a good Vayne can destroy a decent assassin even without wards or help from team mates.

So, this prompted a thought I've had, well, a belief I've always held about League.

The way I see it, any champion can be a good champion. I don't see any champion as useless.

So, to challenge this belief of mine I'm having a little discussion.

1. What is the worst champion in League currently? Be it judged by kit, stats, or whatever means one so chooses.
2. Now that you picked this champion, assume that it is played by someone who knows the champion inside out (Think challenger level skill on it). Is this champion still useless in the game against an average player? As in a 1v1, if the answer is a no, then is it useless in a 1v1 against a champion that counters it? (Again, think average player vs challanger player)
3. Is this champion useless to the team? Can they split push? Can they engage fights and win? Can they assassinate? Can they tank? Whatever use you may think of, does it even have one role it can shine in?

Note: The "average" player here would be someone that actually knows how to play the champion even half decently. Not someone who goes and tries to kill turret without creeps at lvl 1 lol (seen it happen)