It has not launched yet, so we can't just say that Libra will be the new crypto king. Although it really has a great potential and the most promising coin nowadays, but we'll see in the future if it reaches our expectations. I still believe in bitcoin though.
libra may have a very large community. or maybe when the release and start trading libra can immediately occupy the top 100 coins. that might have happened because seeing so many large companies also had the development of this coin behind. not only facebook.
If our believe is about Facebook occupying the top position, there is honestly nothing to argue about that because it will surely do the moment it get released due to the large community they will attract like you said, but what I usually argue with people is when they think in their head that Facebook will occupy the seat of Bitcoin, which I still dont know exactly the magic they will use to do so.
The fact that Facebook is popular now doesnt really mean people love them that much, many people have issue with the way they dont protect users privacy, they only use them because of the social media platform they have and because they need to communicate with friends and family through it, but now that it involves financial things, I doubt if people will really be behind them for this, investor would not have much coin in them and whatever money they put into their projects will just be to test it.