3 yrs ago TBonds yield were a tad above 4.5%. It went all the way down to 2.5% around Apr-Jul last yr.
The cap gain would have been approximately (4.5-2.5)x30 (it's a tad below that). Anyone believing in bond bubble would have missed out a lot.
Anyone can believe anything their heart so desires. At the end of the day, the total in their brokerage,whether it has gone up or down or nowhere, is all that matters imo.