[quote=@Xaltwind]
Having multiples of the same type never stopped Gym Leaders! ... Which seems like an odd strategy to test Trainers with...

"I'm going to test your abilities by having a single kind of pokémon that all - for the vast majority of the time - share a common weakness ta you're aware of ahead of time before challenging me!"
[/quote]

I kinda wish gym leaders in the games based themselves around strategies or themes or gimmicks instead of singular types. 

Like having a gym leader who uses weather, one who specializes in Double Battles, another based on Sound based moves, etc. A Trick Room gym leader maybe? A Terrain gym leader would be cool. 

Rather than a type, they base themselves on mechanics.