Instead of Noinbat, I would suggest almost any other Flying type (even Fearow). It just can't take a hit. Regaurding Yanmega, in my case, I had my Frogier and Zebrastrika (2 special attacker) doulbe attack it, and take it out before it attacked (otherwise it caused too much damage) Since Rosalia knows Giga Drain, it should be able to one shot Anorith.
I would definitely say Geodude. From my experience at least, Slugma was too slow to get off an attack 80-90% of the time. Fire attacks are useless in this gym (unless you can outlast Rain Dance) and Slugma's rock throw didn't really do much.