You're half correct, that's not a test of skill.
What's supposed to be the test of the player is whether you end up in the situation of needing to backtrack to heal in the first place.
There's only two major ways to have difficulty in a JRPG like classic pokemon. Either you have every battle be ballbustingly hard to the point where every single battle can potentially be a game over (In pokemon's case, a white out), or you have numerous easier battles that wear your resources down a little bit each and may force you to retreat to heal. Obviously option 1 is never going to be the one they go for in pokemon, so it has to be option 2.
The entire gameplay loop of the single player modes is about whether you've adequately prepared by bring a sufficiently varied team to deal with what you came across until the next safe point, typically meaning the next pokemon centre.
This entirely falls apart when you can access all your pokemon everywhere because not only does it become extremely difficult to lose because in general no single AI battle is going to knock out all your pokemon, but even if they do manage something that might have previously whittled you down little by little, that's now impossible because the moment one of your pokemon is knocked out, there's no reason to do anything but immediately swap it for a fresh one at no cost in any form of resource, time, or effort from the player. This is compounded by the now permanent exp share meaning you have a glut of exp and pokemon that are constantly overleveled, even in remakes of older games.
That's real tedium, because now every battle is functionally pointless as there's no real way for the player to lose out in any meaningful way, no matter what happens.
With any luck, Arceus has rectified this.
