I dont really see to be a competition against BTC and other altcoins in the market yet this is most likely to be similar with those stable coins we have seen in the market.OP is definitely talking about Libra and we have seen how this token is being stopped or being blocked by the government or lots of critics and problems been faced yet they do saw for this project to be a threat to them.Anything that cant be controlled by the government would really be always getting different treatment.We know on how big facebook is and so as with the government.
At this point we do not really know if Libra is going to launch at all since it seems most governments want to block it, which is not surprising, if people begin to use a coin created by Facebook then some of the most powerful companies around the world will decide that it is in their best interests to create their own coins and suddenly things could get out of control for most governments, but as you say that Libra coin will not be a competitor to decentralized currencies like bitcoin but it will be a threat to stable coins and fiat.