The deflationary fixed amount of BTC is certainly enough of a "fundamental flaw" for me. I don't think you need to be an economist to recognize the problems inherent in that.
"No credit" is an exaggeration: gold and silver (and notes redeemable for gold and silver) were the standard currencies in Europe (and probably other place) for many centuries, during which time there was plenty of lending and borrowing going on.
For most of that time, the total quantity of gold and silver in existence remained approximately constant.
"Systems" are irrelevant to the discussion of crypto-currencies. No nation ever will have an economy based on BTC. The halfway argument (if a BTC-based economy would be bad, economies exposed to some BTC would be sort-of bad) doesn't work, either: the global economy has survived many other assets that appreciated in value.
Bitcoin isn't supposed to be an asset though, it's meant to be used as a currency. Unless it's no longer a currency, and the bitcoiners have all changed their tune.