>>57531973Honestly, Gen 2. Everything in Johto kinda sucks, apart from the Japanese vibes.
Johto is flaws and not much else redeeming them beyond 2 regions. Out of any of the GSC or HGSS options available, it's a struggle coming up with 6 viable mons that have any type diversity, let alone anything you're getting before Badge, say 7-8. You're reasonably looking at Cyndiquil to start, since HMs and GSC being pre-Physical Special Split really hurts Totodile and Chikorita is... Well, bad. Ampharos is your only realistic Electric option, and the pretty large number of stone evolutions that take up the dex are locked to post game. In fact, a lot of the good mons here are locked to the post game.
Level Curve pre-Gen 5 has always been an issue, but wild Pokemon are insanely low. Adding new team members from the already incredibly small pool of feasible mons is made even harder.
The Gym leaders also suck. Most don't have Johto mons as Aces, and some don't even use new mons at all, like Morty, Busy, and Falkner. Lance is also a lackluster champion, 3 Dragonite. Half of his team is weak to Electeic, think all but Aerodactyl weak to Rock, too.
I don't know that I'd consider Johto the weakest games, I'd probably give it to X/Y, but they're certainly pretty low down.