Hunting is the best way for myth farming. The key is that you have to be in a hunt party who is willing to look for the hunts instead of waiting for them to be announced. You can still do roulettes and those do give a good amount of myth tomes, but in terms of myth gained per hour, a good hunt party is better. Keep in mind with the recent patch though that you will be only looking for rank A and S hunts. Rank Bs are almost worthless unless you have a mark bill.

Frontlines is actually very popular on the JP servers. It's difficult to queue an entire 24-man pre-made in to Frontlines which is why it hasn't taken off so well with the pvp guilds. There's also little reason for players at end-game to want PvP equipment obtainable from Frontlines. I think the battlefield control is pretty fun too, but it doesn't help many players progress or get glamours, so it only appeals to the niche group who are already done with or uninterested in progression.