Quantitative Easing swaps a long bond for a central bank reserve that gets stuck on a commercial bank balance sheet earning IORB
treasury buybacks swap a long bond for a money like Tbill that is the most liquid and modular collateral that exists
Size of operations aside, you can make an argument the current program being at least as equally potent.
Especially if Fed were to begin buying those bills, then thats outright debt monetization indirectly.
Just some thoughts