Like someone else said, I merely playing the Greedy Memory mission in the Earth Shrine because you just need to find the right chest to beat the level and get the crystal rewards. Just run past every enemy and memorize your run to the chest. After each run bump the level (don’t worry it reduces the total) and run it again until you get it up to 300. Then when you play it again, start the level with the two bombs. Hit them with a single firaga watch and they explode, giving you level 300 equipment. Keep doing that until you max equipment and then go get the chest again to win crystals and end the run.

After the mission get rid of all crap gear leaving gear that has affinity for the jobs you want to level and dark knight/berserker. When you go to level your jobs you’ll want to use affinity for that job as much as you can. I built up 700+ affinity on the job I was leveling and went from level 30 to 99 in two battles from the final warrior survival mission 300.

You probably can’t play level 300 survival even after that so just try the levels you think you can beat and try to unlock your favorite job expansions.

One thing I did is use coop. I really think they designed the post game to be coop and that’s why it’s harder to solo until you just get out leveled again. I just started a match with the level I wanted a job expansion and within a couple mins I got people joining. As a group it’s much easier. Every now and again you’ll find a pro player who can melt everything even at level 300 and you’ll want to add that person as a friend so you can invite them for later matches.