The doubt is but obvious because crypto currency as a whole including BTC + ALTCOINS together is not even amounting to the trillions or so and thus it is just little toy in a big toy shop. It may not even impact it because it is global stuff, and traded all over the world at the same time and hence also gets too much diluted over the time.
This is why crypto may not have any impact over the global Economy whatsoever.
If we are going to go with the word disturb, it already has. There are already banks and investment firms who are trying to adapt to the new system, there are companies who charge 3% for any transaction you might want to do and people will select those less and less in the near future, there are banks who can transfer your money from one country to another easily without charging that much, even from one bank to another bank.
Hence, bitcoin managed to disturb the money transfer systems, there are blockchain companies now who are disturbing the way data is stored and they are using blockchains p2p system to keep those information and data in there forever no matter what happens to the location they are based, and also making it reachable anywhere they want.
Basically bitcoin and crypto managed to disturb a lot but just not as much as we really hoped.
What all of us missing out when calculating what the global market is and what crypto market worths and all that is the fact that crypto is not shaping up just "buying and selling".
I understand that finance world is HUGE and it is hard to break into that but the fact that crypto and blockchain chan move onto many other things shows that crypto doesn't have to break some sort of financial record in order to disrupt the world. Blockchain is used to make games, blockchain is used to keep records, crypto is used to make ICO's and make more crypto, bitcoin can be sent for just couple dollars even if the amount is over a million dollars (which many companies charge thousands of dollars). Basically there are so many places crypto can touch that finance is just one part of it.