The future of finance is in some future crypto that provides for economic-growth-based inflation/deflation of the money supply. The Fed does this manually, and that's what keeps USD more-or-less stable.
That is wrong. Maybe you mean 'fixed supply currency'.
There is nothing inherent in deflation, defined as 'general decline in general price level' that makes it volatile in terms of purchasing power.
The old pre-WW1 gold standard was deflationary, but it was also as stable as any system humans have ever come up with. It worked by banks adjusting reserves depending demand for their base currency.
...and yes, Tether is far more used than Bitcoin for non-speculative trading.