While hardly on topic with a new Zelda game discussion:
It depends. Tiers are great and all, but for semi-casual, semi-competitive play I was able to use her like a champion and was (not to toot my own horn) able to school the people I played with or at least keep matches competitive. I never really used Sheik, if I did, it was by accident and maybe rolled with it till I could get away and change back. I'm not and usually not a part of tournaments, so I can't guage those players and tiers but from my personal experiences with my group; either way I found her really enjoyable to use, tiers or no (but if you do want to go on with tiers, of the higher ranks I also rock ass with Toon Link, Ice Climbaz, and Marth).
I also hate tiers because you can use the "lowest tier'd" character against a "high tiered" one, a level of skill does come from the player. If someone sucks dick at using Meta Knight, then little is going to help you from owning the battle field if everyone else is simply a better/experienced player. ((again, I'm saying this as a tounrey-avoider)
Petty issue: I actually get annoyed with players who stick to one character, I also like to think of myself as a player who is a "jack of all trades", but master of none. I like having fun with a bit of everyone.
And with respect to letting Link jump, too many games made his jumping contingent on an item that makes him jump.
And I hate that, it wastes a slot and shouldn't be that big a deal to implement (could make for a new adjunct to gameplay).