Seems to me that more mid-majors are having tournament success now than ever.
Agreed. My theory is this: mid-major coaches have to be creative and ahead of the curve, given the obvious disadvantages, relative to the P5 schools, out of necessity. There are always going to be changes to rules whether its on the court or off of it. Good coaches find the opportunities within the rules and adapt to gain an advantage; usually with some risk. A P5 coach doesn't necessarily need to take the risk early in the new rule's life cycle. But once a coach has success adapting to the new rule, others mimic it and it gradually makes its way to the P5 schools. Everything goes in cycles.
Example- the A's followed the 'Moneyball' philosophy because they couldnt compete with higher spending clubs. They needed to find a way to level the playing field and Moneyball did just that. I'd argue that using a Moneyball approach ended the Red Sox and Cubs World Series droughts. It took some time, but now all most all MLB clubs are using data as a tool to shape their player development systems. Some more than others, but they all are using it.
the spread offense in college football was created out of necessity. the non-blue bloods knew they couldnt line up with the Alabamas and Florida States of the world back then. They knew they could recruit quick receivers but the big linemen werent usually going to play for the Texas Tech's of the world. So they recruited more of same type of players they knew they could get and adapted their offenses accordingly. Years later, the spread has become a staple of the game.
Coaches at the mid major level that can find opportunities in the changing landscape will have success. They have to find those opportunities; if they don't, they can't win and end up looking for new jobs.