>>52126601outsider anon here, just been following the conversation. What about a third option, where with levels comes tactics?
For a base assumption, take a completely open world game, challenge most of the gyms in any order, outside of maybe the first and last, for consistency. Each gym you beat ups the difficulty of the next, from adding more Pokemon to the teams, higher levels, to them actually using gimmicks like hazards, status effects, and the like.
Outside routes should still be locally scaled, though more Badges could possibly either increase the range of Pokemon that appear, or give chances of stronger Pokemon appearing as a challenge for the area.
There's a middleground where you can scale gyms/encounters to the player, without making it just a numbers game. Maybe the Fire Gym is just a statcheck in the first 3 fights, but after wards starts using Sun strategies? Poison Gym that uses Stall tactics if you come at them last?
And, most importantly, you can make this scaling into an optional setting, so the kids can have an easier time.