Octopath Traveler: About swapping party members

[Peh]

Yes, this seems to be an issue at first, but after your party is above level 50 (I'm at 64) you can easily tackle everything with 3 characters. So, just put lower level character into your party, go some monster hunting on a field with lvl 58 monsters and see him catching up to your party actually very quickly. You can try to use the dancers ability of increasing EXP by 2x or 5x if you are lucky.