I think in value the bitcoin is the major currency but no body can calculate the exact amount and transaction s of crypto i believe that it is not transparent like dollars and pound etc so that's why it can not be judged accurately and for me it is the number 2nd currency after Dollar.
It is pretty hard to calculate the same for euros too. Countries mostly calculate what happens within their borders (GDP) but have a hard time calculating it globally. Only Us has a better idea since all US transactions go through US corresponding banks, but it is not the case for pounds or euros.