Yea i agree that Unova's layout is rather messed up with little/ no training time between Nimbasa and Driftveil, but i never found my team severely underleveled.
On the subject of mixing up gym types i will voice my opinion : To make gyms a little less predictable all they have to do is throw in a unexpected dual type e.g. Skarmory with Skyla.
The striaton trio are not a great example to go by as they weren't overly powerful to begin with, and due to the fact you are given a pan-monkey superior to that of the leaders, it defeats the purpose. They don't need to go the extreme like with blue, but they could mix things up a little with movesets to make it more challenging.