pem
as for it being a big assumption, I dont think it is.

when was the last time passbook savings rates were more than 4.75% and did they stay that way over a 30 year period? I dont think CD rates have been much higher than that over an extended period either. I’m sure there were times they were (heck my parents locked up 15% rates in the hyper inflation days which lasted several years until they got called) but show me long term rates higher than that from banks.