"Are you arguing that it's a good investment vehicle"
For an investment, it's up to you to determine that through the accumulation of knowledge and wisdom. This contrasts current societal norms which rely on appeal to authority (eg. Financial Advisor orthe failed Segwit2x) or social signalling through marketing (eg,The crypto s**t storm of 2017, Bcash Roger Coin, ‘Blockchain not Bitcoin’ non-sensical slogan, or the dot com bubble) or social signalling through religious false deity marketing(eg. Craig Wright).
"or that crypto could be used as currency?"
It already is used as a currency. Currency simply means 'medium of exchange', and there are many places and people which accept it for goods and services. For example Overstock.com or Tone Vays for his conferences or courses. This medium of exchange market remains extremely niche, and will likely continue to do so into the short to medium term as easy money (Fiat) is expended, and hard money is accumulated. As humans in the market, there is a natural incentive to spend or consume the goods depreciating in value, and to accumulate goods that are increasing in value or rare.
"I'm just looking at it from an economic point of view."
I'd recommend reading the Bitcoin Standard by Saifedean Ammous for a deeper understanding. You also seem to be approaching economics from an assumptive and non-praxeological standpoint. Real economics is the study of human action and behaviour in the market. Current establishment keynsian ‘economics’ is the collection of aggregate data to contort into whatever narrative the state requires to justify its own actions. The state also has the added benefit that when the meaningless aggregate data ‘goes off the rails’ (As is common), it can use the explanation of ‘animal spirits’ to explain the supposedly unexplainable results.
"You need to be able to control the amount of money in economies to effect monetary policy specific to a particular economy,and relative to other economies through exchange rates."
No such requirement exists for the long term improvement of individuals well-being across mankind. In fact, the nationalisation of money has created the following negative detriments:
Enormous waste of resources in the Foreign Exchange Market – Currently the largest market on the planet, but was not even necessary during the days of the global gold standard. This diverts purchasing power away from individuals who could have otherwise purchased goods to benefit their lives and improve society and into the wasteful process of converting from one type of currency to another. The nationalisation of money almost takes us back to the pre-money barter stage of civilisation for international trade.
The ability for Governments to inflate the money supply and therefore steal purchasing power from individuals is theft. Inflation fundamentally being a form of taxation without representation or due process in law.
Barriers to global free trade from the Foreign Exchange market creating a systemic misalignment of incentives and resources
“One way out of it would be for Europe to have a common reserve bank to equally distribute money throughout the EU”
This statement is a testament to your complete miscomprehension of economics. How on earth would a European central authority (In this case, a central bank) make the determination of which regions required more supply and which ones less?. A Governmental body is by definition not ‘market connected’ to its direct actions on the market, due to its monopoly of force on markets. This reality creates numbness to price signalling (Bad or good enterprise is no longer punished or rewarded by market forces, but by appeal to authority and other artificial means).
“Similarly for crypto, there would need to be a common reserve bank for the entire world, fairly distributing wealth across the globe in the best interests of advanced and developing economies...”
Such a system is neither needed nor desired. Reserve banks (And Government departments in general) are disconnected from the direct consequences of their market actions by design. In rare scenarios it may be possible for an individual’s actions in the Reserve Bank to be held to consequence from their actions, but the reliance on artificial means (Appeal to authority, appeal to emotion, social signalling, etc) makes this a highly unreliable mechanism.
Bitcoin’s monetary inflation mechanism is an openly known mathematical reality which continues to decline to zero. This enables market participants to operate in a monetary free market, without Government interference and theft which would otherwise create systemic misalignments of incentives and resources. The monetary ultra-low inflation (And eventually micro-deflation) creates an incentive to accumulate the asset. However in contrast to the views of mainstream economists, this does not mean people will hold onto their money forever and die of starvation (I sometimes can’t even believe they print this). But instead, they will simply give second thought to what they spend their money on. This is called lowering ‘time preference’, and it enables savings,building capital and improving society. The inverse, high time preference encourages the opposite, expenditure with little thought and debt slavery.
