Didn't I just recently have a conversation on Rain's viability...?
Anyway, it's not that Rain is a terrible character...it's just that each and every single one of the common tournament characters could excel at what he does at far greater levels. Not to mention the dash nerf only worsened things, although we had dash-blocking to compensate for that.
These things are what hold Rain back from achieving a top-tier status:
1. Large hitbox which makes him vulnerable to strong pressure games.
2. Inadequate zoning, forcing him to stay at least half-screen range to be effective.
3. Somewhat slow normals.
4. Shitty teleport...okay, it's not too shitty, but it's certainly no Raiden-styled teleport.
5. Sub-par poking game.
6. As already pointed out, all top-tiers can do what he does, and they do it better.