i think what makes routes from earlier pokemon games challenging is that, when you're midway through the route and your pokemon are at low HP, it's not ideal to backtrack to the last pokemon center because you lose a lot of progress (and you have to make your way through wild grass again). so you might want to just use potions and keep pushing forward.
in newer games, there's really nothing stopping you from running back to the pokemon center every 5 minutes (if you even need to) because there are practically no obstacles in your way
