I really don't see how you could simplify it any further without entering "press a to win" territory. Anyone who finds pokemon too complex should probably be sterilized. I say that unironically.
People complain a lot about there being Physical and Special damage and the stas being too divided up. Also they don't like that Pokemon have different stat distribution or that pokemon can use move of a different type they are. It is really stupid, I guess that's why some people claimed that Yokai Watch was better, because that game plays itself. That's the future.
The game now tells you it through little labels wether an attack is effective or not (altho you need to defeat the pokemon you are fighting first) and even they are still crying "Too complex!".
Pokemon has always had a sort of fluctuating difficulty. Overall, I found Gen I to be fairly hard, Gen II to be fairly easy (except for Whitney, fuck Whitney,) Gen III was alright, Gen IV was fairly easy right up until the Champion fight (where I had to eventually go on the internet and trade for a level 100 Snorlax,) and Gen V was fairly hard but also fair.
Ignoring simply not being able to "git gud," the biggest problem with difficulty is fairness. I don't mind super hard games _that much_ but I hate unfair games. It's the difference between, say, a well designed Super-Expert difficulty Mario Maker level and SMB 2.: The Lost Levels. Example of the former tend to feel like every death is your fault, while the latter makes it feel like the game just screwed you.
They are all easy. The difficulty comes on the competitive side, yet many people (who don't even engage in competitive) want GF to simplify mechanics just so they don't have to think too much.
On the other hand, a game can be unfair to itself, and that can feel crappy, too. If you're just storming through a game from beginning to end without even thinking about it and with no real difficulty at all, that also feels crappy.
Gen 1 was artificially hard, kinda like how Final Fantasy 1 had certain difficulty spikes because of broken stuff. Gen 3 was fairly hard, but not absurdly so. Gen 5 suffered from difficulty spikes up the ass.
In Gen1 you just needed to get an Alakazam and it would take you throug the entire game. It has the highes SP Attack, can learn a lot of tm, nothing hits him Super Effective (Ghost did no damage to Psychich in gen 1 due to a glitch and even then the only ghost moves were Lick and Night Shade, the first very weak, the second always doing fixed damage).
Nothing resisted Psychic before the introduction of Steel and Dark thus Alakazam was unstoppable. Gen 1 is only remembered as hard because the people playing it were children.
You can only get Alakazam, though, if you trade a Kadabra, which means that if you don't have any friends who play Pokemon (which was the case for many) then you'd need to get two Game Boys, two copies of the game, and a Link Cable. For most kids (and even a lot of adults,) that's a tall order.
When was the last time games being unfair because of the difficulty? I know Soulsborne series are absolutely fair, to the point where there being people who claimed the game's not hard/difficult at all. Again, let's go back to that Cuphead example. Was the game being unfair at all, even with the simple tutorial? I've watched the gameplay videos. Difficult looks of it, but nothing unfair from gameplay perspective.