Yeah, money velocity is important, aggregate demand is real, and currency hoarding is unavoidable with a deflationary currency. Why buy something when you can buy more somethings tomorrow?
In anything technology related, this has already been true for a couple of decades now. I can buy a phone, TV, computer, tablet etc today, or I can wait a year and get much more for the same amount of money.
People still buy all of those things because, as others have posted, you reach a point where you just have to or want to upgrade because the alternative is you spend years on old technology endlessly waiting for "just the right time to buy".
https://www.theonion.com/chipmunk-s-plan-for-future-better-c...
You also reduce risks by paying taxes in the same currency you conduct business in. So, while having large savings in deflationary currency is not a great idea, for the average person deflationary currency's are surprisingly appealing.
PS: Remember, many things like socks are valued in USD, but are not actually USD. Total USD supply is actually fairly low per person limiting average losses from inflation.
But all else isn't equal. Since the deflationary one induces people to horde, you might have sudden, extreme inflation if people panic sell.
Bitcoin and other crypto are only deflationary if their economies grow faster than the supply. But that isn't at all guaranteed.
A mortgage, a car payment, becomes more expensive over time since the deal was struck when prices were higher. A bitcoin can buy you a heck of a lot more now, but the mortgage you signed in 2014 was for 200 bitcoins. Uh oh...
Now, of course you can argue the necessity of credit until the cows come home. The bottom line is whatever credit is to you, deflation really throws a wrench in it.
Naively, other things the same, the best time to take out credit for something you need is now. Under a deflationary currency that time is never.