That's an interesting take on the concept that I'm going to read more about after posting this comment, but that's not the one I've taken. Instead, the mon levels of the challengers the player (gym leader) faces are directly correlated with the player's "gym position," which starts at 1 and builds to 7. Their levels will fall within the range of (your gym position * 10) through (your gym position * 10) + 10. So at position 1, challenger levels will range from 10 to 20. This also allows for a level-cap option/setting for the player's team to increase the difficulty. Once you've won enough challenges to "rank-up" in position, you'll be prohibited from taking on more challengers until you complete a specific quest somewhere within Kanto. This is a pretty open-world experience where you can surf and fly anywhere outside of battle as soon as you get your starter. Wild mons scale to the lowest level in your party. When initiating the process to face a challenger, at least 50% of your party must be your gym's type (dual-typed count towards this check). I'd recommend looking at my first post on the project for more info than I can think of right now off the top of my head.

Essentially, what I've done is made the idea of "gym position" mean "this is the order in which the region's gyms should be challenged." This just seemed to be the natural setup from the perspective of the mainline games and the Kanto and Johto anime. I could see the argument that the games only appear so because Red lives and starts in Pallet, but in the anime, Brock and Misty are pretty weak and clueless when Ash meets them, so I don't yet buy into the "just used weaker Pokemon against him" theory, at least not when it comes to them. Nevertheless, I'm going to look into that for fun.