TBH I've been replaying Red and I really don't find it challenging or that tedious like some people claim, it's about as easy as the modern games in my opinion---sure Trainers have more Pokemon but they aren't really smarter, the ease is more in the QOL improvements like less time spent having to head to the Pokemon Center. Otherwise I'm breezing through it and keeping my team balanced without much extra grinding, though I do think it's a bit more difficult in terms of knowing where to go---and I kind of like that openness.
It largely depends on what Pokémon you have on your team but for the most part I disagree as I recently played Pokémon Yellow and Misty, Koga, Sabrina, Blaine, Blue many times and quite a few trainers have given me troubles.
Game Freak have change up the game design making it easier like how none of the Gym Leaders Pokémon have 4 move set till the 7th gym leader, The Elite 4 all have 4 Pokémon each, Kalos being super simple to navigate with no secret's areas to explore, with OR/AS straight up changing the game play so that the players don't let lost, again with OR/AS straight up giving players a powerful legendary Pokémon packed with a Mega stone.
The only time that I have ever struggled against a Kalos Gym Leader is against Grant and that's only because my teams lacks a strong fighting Pokémon to quickly take out Amaura before it fires a Thunder wave.
Now I get why Game Freak lowered the difficulty so that new comers and younger players can play the game and that's 100% fine but all I am asking for is that Game Freak to do a better some in teaching and encouraging players to explore the region at their own pace and discover new Pokémon, pick up useful items and TM because at the moment it's at 0% which means future region designs are going to get worse and worse with exploration being absent.
I also believe that with the Exp share acting as easy mode I think that it's also fair that Game Freak also bring back and refine challenge mode but have it that the players unlock it after defeated the first gym leader so we can avoid players accidentally picking challenge mode when they start the game and if they do pick it and find it hard then they can easily turn it off.
I just feel that ever since Game Freak got feed back that kids didn't finish the Sinnoh game because they found it "hard" they have been reluctant in handing back exploration and that sense of adventure to the players.