Absolutely not. UST was offered as a “stablecoin”; it is an obligation, a liability now due and owing. UST has a promised value of $1.00—no more, no less. LUNA has no promised value whatsoever—and yes, it can even go to zero. In this context, LUNA’s only promise is that it is fungible: Each LUNA is equal to every other LUNA.
I can’t believe that I even need to explain this.