It is not even remotely difficult to get from 50~60 on alts, I leveled up WAR after my SCH and all I did was roulettes, a little dungeon grinding, and maybe 1-2 levels of FATE grinding. If you are tank or healer spam dungeons ESPECIALLY Gubal Library from 59~60 and it goes by very, very fast.

If you are DPS do your roulettes, then queue for a dungeon appropriate for your level while you spam leves or FATES. I like to do a few Temple Leves because you can get Amber Encased Vilekin which you can trade for appropriate-level accessories and they also give a nice chunk of EXP. They're a little tougher but if you bust out chocobo they're manageable, just keep an eye out for silver chests.