Are you trying to claim it's a bad deal for the mortgagor? That is a claim that's going to require quite a lot of evidence.
Long-term fixed rate is still a relative rarity globally, especially in the US style where there are no prepayment penalties. France is a notable exception, as specified in https://business.sdsu.edu/research/_files/_realestate/intern... , but still doesn't have the prepayment-penalty-free nature (though prepayment penalty amounts are capped by law).
I was pondering that tradeoff myself two years ago, having retired early from crypto. The only issue is, to get the 2.5% you had to show Fannie Mae-acceptable regular income. Which is still possible: the FIRE people have a system for putting your money in a trust that pays it right back to you[1], then waiting two months to establish a history, and then you dissolve the trust once the mortgage is finalized and you've closed and moved in.
I would have done that myself except that it would involve putting a big delay on my search. Early comment about it: https://news.ycombinator.com/item?id=31000286
[1] https://old.reddit.com/r/fatFIRE/comments/ojs18l/obtaining_a...