Yes I've played RS3 though I've not finished it completely. I remember vividly that main characters appears on each other's scenario and some knows each other. They're all part of a similar conflict and some are related in many ways. Some playable characters are also part of sidequests that leads to their recruitment so they're definitely a part of this world, too. You can't say they don't know each other story-wise, even if they hardly interact between each other. The limitations of a non-linear JRPG didn't prevent them to add a myriad of ways to follow characters. Romancing Saga 3 is most likely going to be on switch in less than a year from now so it'll be interesting to see how players who played Octopath will see how RS3 stacks up and how different it is.
Aside from the intro quest, the other main characters do nothing.
Yes they do know each other, but knowing someone doesn't mean you'll go together in a quest to kill 4 Legendary Beasts.
If let say you pick Julian as your main, you can recruit everyone except for Katrina.
How you recruit them: Find their location, talk to them => Instajoin
There's nothing explaining their motivation or their personal quest.
I also brought up "issues" with other non-main characters: The girl with 1000 names, Bard, Zo, Boston, Yuki, Nora, etc.
The way I see it, both OT and RS3 focuses more on the gameplay aspects and sacrifice "immersion" aspects.
Romancing Saga 3 is one of my top SNES JRPG, so I'll be awaiting its English release hopefully this year.
Looking forward to see the reaction from ERA, though judging by how quiet the reaction to RS2 is (the OT hasn't even reached half the page count of this preview thread lol), I'm not expecting much to be honest.