If you notice I put a double-quote for the word "interest" MAS also never use this word. It is a discount. But to layman who are used to FD and would like to compare it's equivalent "interest" is something that they understand.
My point is the upfront refund mechanism of t-bill is not economically better than FD.
For t-bill, upfront u pay Principal (P), and upon maturity u get back Principal + Interest (P+I).
P is 100 minus upfront refund. P+I = 100.
For FD, upfront u also pay P and get back P+I upon maturity.
Just that for FD, P is typical some nice rounded number like $10k, unlike t-bill where your P is $9812.
End of the day, both t-bill and FD are bullet pay-offs i.e. u put in a lump sum upfront and get back that lump sum plus interest at maturity.