>>55651406novelty mons meant solely for collecting or gimmicks are fun, the problem with sinnoh and johto that leads to samey teams is that your options are split cleanly between strong, reliable mons that will carry you through the entire game with little effort and novelties that suck shit in battle and are just meant as something for the player to collect.
sinnoh has some mid-tier mons, but they're locked but their encounter methods require time and/or effort that they aren't good enough to justify.