Gen 2 was fun, but the level curve was terrible. I thought that as a kid too. It felt like once you reached mid 30s, nothing else went beyond that and you were fighting things that were mid 30s for the rest of the game.
And really with only so many pokemon to draw on and the regions being right next to each other, it's only natural to have Kanto pokemon available in Johto.
The problem wasn't that Kanto Pokemon were available in Johto, that actually made sense, the problem was you had many Johto Pokemon who could straight up not be found in Johto and you had to go to Kanto to get them, or you had to jump through some crazy hoops if you wanted to catch them, whilst on the other hand the likes of Pidgey and Rattata(that damn meme) were rampant.
It didn't help matters that half of the gym leaders, namely Falkner, Morty, Bugsy and Chuck, didn't have a single Johto Pokemon on their team, and the bulk of the other 4 Gym leaders teams were made up of Pokemon from Kanto, though I'll give Clair a pass since Dragon types were rare as fuck back then.
You can't even begin to imagine the disappointment when 8 year old me discovered that I couldn't get Houndour until far later in the game, the salt has been pouring since then