I never really had a problem keeping my party properly leveled in Octopath Traveler because 1) they give you the level for each character's next chapter right after you finish the current one, and 2) you can easily get all eight secondary classes at the start of the second set of chapters. The game gives you enough information to know who you should be leveling in the short-term (because their chapter comes soon given the recommended level), and enough flexibility that you can have any character in your party at any given time and not be hindered all that much (outside of some boss battles).
If too much time between chapters is a concern for you, the game also gives you enough flexibility that you can make two separate parties and just run through all the chapters for one party before moving onto doing all the second party's chapters. I didn't do this myself, but I saw quite a few people say it worked well for them with a little bit of planning.
Also, I don't agree with H'aanit being useless without monsters at all. I ignored that mechanic for the overwhelming majority of the game, and she was still one of my favourite characters. Hunter class skills are great both for boss battles and for speeding up a lot of normal encounters (which, yeah, it doesn't surprise me normal encounters are taking you a long time if you think she's not super useful).
As for the structure of the game overall, I thought they did a great job delivering on what they set out to do with Octopath. As Clex alluded to, it really feels like you're on an adventure with eight travelers and the game lets you go about it in so many different ways. I had so much fun with the battle system and building up characters and parties, and just exploring the world and the towns playing as all eight characters as I went. On the flip side, if you wanted to minimize the time between each character's chapters, the game is structured in a way that makes that approach feasible too. It's a super unique and enjoyable experience that stands out to me even like half a year later.
The game sold over one million units in less than a month, and that's with shortages in Japan and in the West, so it was definitely a commercial success. Asano has since said that BD11 is expanding and has hinted that they're currently working on multiple projects (and have heavily teased another Bravely game), so it definitely seems like Square Enix was happy with the result overall.