Based on what? The talent gap has gotten alot further now. Mid majors can't build a program based around 3 or 4 year guys anymore because their best players leave now for NIL.
This tournament is a shining example of this. The upsets just aren't there anymore and many games were non-competitive.
The talent gap is not further now. No way. You're focusing on this year's Tourney alone. Upsets may or may not happen in a given year. And fewer mid-majors got in this year because the committee decided to put the entire SEC into the tournament.
As for your mid-major example: they have a lot more flexibility in building their rosters now than before just like everyone else. They can backfill with better players overall up and down the roster.
Colorado St should be in the Sweet 16. UCSD played Michigan tougher than A&M. The Bryant roster has guys who previously played for power conference schools as do many rosters of other similar schools.
And really, even though it's been a chalky Tourney, the mid-majors who lost were more than competitive and usually covered.
This year's Tourney's been an anomaly really. The previous 4 post COVID tournaments (all with NIL) had:
2021: 15 seed lost by 2 in the Sweet 16
2022: 15 seed made the Elite 8
2023: 16 seed upset a 1, 15 seed made Sweet 16
2024: 14 seed went to OT in Rd of 32.