I mean I kind of disagree with this. Pokemon games got slower. Not that the first couple were speed demons or anything, but they got progressively slower. Gen 3 is when it started getting noticeable I think as op is mentioning here, Generation 4 was downright excruciating.

Biggest tip I have is playing an emulator so you can up the speed. Pokemon games as they progressed got slow. And I don’t mean just the grind I mean like the game play itself like shit took longer. Moves and every little animation took longer to happen. Jesus Christ doing HM moves by like the Gen 4 were just excruciatingly slow I had to stop playing. Absolutely emulator double or triple speed helps tremendously.