You see other adventurers at the beginning of Wanderer's Palace, and then again in the Endless Rise getting attacked by tonberry stalkers. (Not sure if it's meant to be the same people both times, or if there are multiple parties, but you meet the one couple afterwards in the hard mode unlock quest.)

You encounter tomb raiders in Qarn hard mode, and they're the ones who set off the traps and endangered the researchers you were sent in to find.

There are also adventurers out in the field at Mor Dhona, particularly as FATE NPCs fighting monsters.


It seems to me that a lot of "adventurer's jobs" are more the stuff we do in the overworld - defeat monsters that are a danger to villagers, fulfil guildleve requests, do odd jobs and deliveries for some extra gil and possibly food. We've just been drawn into this bigger conflict that's far above and beyond what the average adventurer would (or could) be doing.