Even leaders use some non-high tier Pokemon. It's more about strategy than raw power. Keep in consideration that leaders can prepare for you and they choose between single, double and triple battles.
Mmm, another thing I've got to get right is making the team good for doubles and triples without crippling their singles ability too much. I have some fun ideas, but the hard part is getting team synergy at the end. It is for me, anyway.
That's good to know.