cy made a comment that there's a trend. You decided to cherry pick some of your own parameters to overlay on his statement (% of teams reaching the top levels of the tournament, limited to the last 10 years only as a single data point), and then complained about manipulating stats. lol
You only want to look at a single data point to prove out that there's no trend. A trend needs to show change over time - that means you need to have a "before" state to compare to. If your "now" state is the last 10 years, then the "before" state has to necessarily be before the last 10 years.
It seems that you're trying to argue that "right now schools from P5 conferences are dominant" (which I don't think anyone is disagreeing with) in opposition to an argument that "overall P5 dominance has diminished over time". Those are two different arguments.
If anything (specifically with regard to the single data point of teams reaching the Elite Eight) tournament success in the major conferences has condensed somewhat to the top teams, at the expense of the middle teams. In the last 10 years, about 37% of teams in the current P5 made it to the EE. Over the prior 10 years, about 45% of teams in the current P5 had made it to the EE.
To really look at this, though, we'd need to take into account a lot of factors. Top 150 recruiting commitments, tournament success, head to head regular season and tournament records between major and mid-major teams, # of teams finishing the season ranked, # of players in the NBA from major vs. mid-major teams, etc. And they'd all need to be looked at over time (80s vs. 90s vs. 00s vs. 10s, or whatever) if any real trend was going to be proven out.
From the very small window I've looked through, though, my initial feeling is that power is consolidating more at the top of the major conferences, while the middle/bottom of the major conferences are seeing more competition from mid-major programs. Which would imply that a program's conference affiliation alone is not the advantage it may have been in the past.