Not so sure I fully agree. Not yet anyway.
Oral Roberts (2021), Saint Peter's (2022), and Princeton (2023) are all 15-seeded teams that recently made the Sweet 16. SP made the elite 8, in fact. Robert Morris lost by just 9 last year over 2 Alabama and 5 guys from....checks notes**...Siena nearly beat 1 seeded Duke before losing by 6. And we don't need to talk about Furman, do we? 14-seed Oakland beat Kentucky in 2024, and in the same year, 13-seeded Yale beat Auburn. 5 12 seeds have won since 2024.
Most of all, we just saw the second-ever 16-seed win in 2023.
Let's see what happens in 2027, 28, and 29 before making any serious claims.