So he "researched" and found a limitation of MW known since 2016. That's $60 well wasted.
https://github.com/mimblewimble/grin/wiki/Grin-and-MimbleWimble-vs-ZCashWhile Grin transaction outputs are fully obscured, it's still possible to trace which inputs links to which outputs at least until some age. But it's unclear at this point what information could be derived from this.
Regarding the
"...at least until some age" part,
I don't understand what the age of the blockchain has to do with this, probably because I didn't understand the exact method of this "attack"
(I don't like to call it attack though since it's not damaging the integrity of the blockchain nor steals anyone's funds).
If I would make a guess, is it because the more people use GRIN and the more transactions are being broadcast, it becomes less possible to trace an individual transaction?