Deflation via credit default has shown to be harmful to wider economy 2x times in US history (monetary shocks). I am not aware of any conclusive study that a deflationary currency is bad for investment and progress. The easy counterpoint is Gold, which is often deflationary (when economic growth outpaces gold mining). We have had 10k years of investment that have shown your basic statement is false (deflationary currency causes investment to grind to a halt).

Inflationary fiat or credit based currency is a relatively new invention (1972 in the US). I have not seen any serious analysis showing that real investment has radically improved since going off the gold standard. Real investment has been growing for decades as real wealth increases, inflationary currency hasn't changed that very much AFAIK.