It seems to me that the "new" privacy technique (Mimblewimble) is completely different from what Monero uses today. Comparing both Mimblewimble coins vs Monero is like comparing apples vs oranges. Each has their own strengths and weaknesses. Depending on your needs, will be the type of cryptocurrency to use for day-to-day payments.
As much as I've used Mimblewimble coins like Grin and BEAM, they're not as user-friendly as Monero is (in some sense). Especially Grin, which is extremely difficult to use for newcomers getting into the world of privacy-oriented cryptocurrency transactions. I don't think Monero will lose its position as the "King of Privacy Coins" because of its first-mover advantage on the market. I'm fine with that as long as people can choose from one privacy coin to another. As long as privacy exists in crypto land, nothing else matters. Just my thoughts