Finished all the elites now, have every spell that i need, including comet for shits. Full group of 50s, new dungeons taking to long qq.
For magitek armor x3 it's pretty easy, just like all the elites, if you have the right abilities. 2x thunder strikes on cloud, 2x thundara preferably at least one honed. Sleep works, use it to reduce overall damage from the fight, aerith limit break is OP and can stop multiple magiteks. The last magitek will be just auto attacks, defend with rydia and aerith when all abilities are spent.
If the damage was spread around enough on your tanks and rydia and aerith take the last bit of damage, you're golden. Do not waste slots on rydia for sleep, sephiroth or tyro are better use for those. You need to have damage coming from rydia and tyro and sephiroth can auto attack fine for the last stretch.
Magissa and forza is almost the same strategy, i used comet in place of my unhoned thundara. Aerith uses limit break at the start of fight to silence magissa, use only auto attacks til forza comes out, sleep and poison forza, unload on magissa til she's dead. use another aerith limit break after sleep wears off or if you don't have another to use, use power break til he starts hitting over 2k. The poison damage on forza was 100% required for me to beat him since i was almost ability-less after magissa died and just defend with rydia and aerith when you can't or don't need to use abilities to keep your melee alive long enough to plink him down.
If you silenced magissa with limit break and used sleep on forza, doesn't matter how many died or how much damage you took, you'll get expert and as long as you championed the rest of the stages you'll get mastery.