It's not necrobumping if you have something to add (which I hope I did). I found this by googling for smogon in-game tiers and wanted to discuss the games when I saw this. I think people are eager to participate in these threads from what I've noticed on these forums, but if you don't care to participate, nobody's forcing you to join.
For Sabrina, I think we can agree that Shadow Ball is a good TM for this gym. Snorlax learns it, and some other bulky Pokemon who could use it for the Psychic gym are Flareon (specially bulky, and his Shadow Ball hits the hardest) and Clefable (whom you have a lot of time to train).
I also think Agatha's strange physical ghost movesets shouldn't be underestimated. If you're not overlevelled, your Psychic of choice will have no chance to attack her Gengars - Shadow Ball is a sure OHKO for Alakazam and Mr. Mime, most likely Jynx as well.