If the zone is dead and you can't fate grind, use the search ability, /sea whm 18 or w/e and ask people if they want to EXP Grind. Find yourself 7 people somewhere in the world and level up with them. Or grind leve's / dungeons until you get through that span.
Imo this game just needs to make the LFG system more intuitive so people know it exists and actually use it.

I miss the good ole EXP Flag from FFXI.....

People don't have to be in the zone to want to level, they might be in another zone. Or perhaps the zone that's active is not the one you are in. E.g. they could be in aleport still, or camp drybone area.

If people knew how to use the search command they would know that you can see where people are the heaviest zone wise for your level range and go level there.