I've always seen this as a weird argument. Most people live paycheck to paycheck and don't have the option to hold even if they wanted to. And those that have extra income will invest it in whatever gains them interest, with the explicit intent of not spending those funds in the short term. I don't see why crypto's deflationary properties would play any practical role at all. Well except that you could actually just hold your income (if you were paid in crypto) instead of having to go through the hassle of figuring out what to invest in.
Edit: But yeah, if only looking at those people who would refrain from investing in stocks and just hold crypto, then yeah, that would leave money out of circulation stimulating the economy. But just overall, for the normal person, it's a moot point.