Fed paying out interest is fully guaranteed. Any other loan posses including commercial risk the lost of principal.
You have a point that the 3% is not a guarantee, but Fed is paying out at that rate.
In my humble opinion Fed should stop reverse repo. They say out right how hawkish they are in fighting inflation. If that is so force the banks to put the surplus cash into treasuries and bonds. This process will push rates lower, hence less inflation.
I stand corrected in some of the items due to my poor choice of words. Yet the numbers don’t lie. Banks are filled to the brim with cash while average American is trying to make ends meet.