I got 100 hours out of Stardew Valley. So by that logic it should have cost $60 too.

It could be. It could be $60 and no one would bat an eye. Except for the fact that no one knows the developer and they practically have to price it the way they do or else no one would buy it. Octopath Traveler is a AAA game and the well known devs are going to price it however they want b/c of that. A game being 2D doesn't mean it can't be full price. That's an incredibly naive sentiment to have. It's all about how the developers want to price it and what you're willing to pay for it. 

The one where you get 25-50 mythril on special events takes 1 battle - which takes a few seconds because you can one shot the enemy even at a low level.

Regular battles with 1 fight takes me 15-20 seconds (unless its a boss battle which could take me a min or two).

Normal battles (that get you 1 mythril) have 3 fights which usually takes me a min or two.

All of my characters are lv 99 (which is easy to get due to experience eggs you get from special events).

FFRK is really easy and not that grindy.


They also recently added a story mode which involves your original character to go into Final Fantasy worlds and experience the game's plot due to the original story's plot.

I find it a nice time sink when I have nothing else to do when I am outside of my home.

Like I said, your results may vary but I built up my party and cast of characters without spending a single penny on the game.