AFAIK, that medium post is nothing new.

Base mimblewimble isn't really designed to be a "black box of reliable anonymity" in the way that Monero or Wasabi-CoinJoins are, where connections are hard-broken. It's more of a framework on which you could build solid anonymity using techniques that have largely not yet been perfected, plus major scaling benefits. Monero = CT + stealth addresses + ring signatures. Grin = CT + "stealth addresses" + mimblewimble. Because grin replaces ring signatures with mimblewimble, its privacy is less reliable than Monero's. Probably the grin developers have tried to make their mimblewimble transaction aggregation methods good, but I currently wouldn't put much faith in it, and IMO it'll take many years of research to get something really solid. That said, CT + stealth addresses offer a certain base level of privacy, and grin's method of handling stealth addresses (using an interactive protocol, exchanging "slates") is both more scalable than Monero and probably more private.

If your goal is to mix coins, grin is definitely not for you right now, and it may never be. Monero's goal is maximal privacy, regardless of the cost. Grin's goal is excellent privacy, consistent with scaling.