Your argument reveals a complete misunderstanding of economics.
BTC is a SoV, just a bad one because its value has been unpredictable until recently. Price of something going up and up doesn’t meant its a good SoV (ex. the many countries experiencing hyperinflation and relying on foreign currencies). Also, I say Bitcoin is not a good MoE because I cannot use it as a method of payment for most day-to-day transactions.
How is Bitcoin “NOT good because it is cheaper to transact”? This sentence confuses me.
As for your question “Who would [use Facebook Coin] and why?”, take a look at the foreign remittance market for starters. Millions of people want to send money across the world without paying a hefty transaction fee.
Unlike your diehard support for Bitcoin (“100% of them ought to buy Bitcoin”), I’m not here advocating people to adopt Facebook Coin. I’m merely speculating what could happen if Facebook releases a crypto. I’m not in support of it or against Bitcoin for that matter. Most of the reasons I share for the failure of Bitcoin are not my personal views, they are the consensus among experts.