Cash and coins are mostly fungible. When you accept cash or coins, there is no record attached showing where they have been.
Monero is probably the best crypto for fungibility, but it comes with a scalability tradeoff (not that Bitcoin is much more scalable though, tbh)
Monero is more scalable than bitcoin *unless* you use bitcoin in a non-private way.
Monero tx size is smaller than than coinjoining.
Perhaps, but neither can hit the 10k+ TPS we need if we're ever to become global money, which I still hold out is the goal of this whole cryptocurrency revolution Satoshi started.
