I actually disagree with this, for a couple of reasons
- Mandarin was in a coma for years between the two incidents happened, we can't be certain he retained his mastery of the rings, considering he HAS forgotten them definitively by the time he becomes old
- This was a hit delivered by his projection, we can't be certain that is 1-to-1 to his own output
- Finally, the impact like, very blatantly doesn't match up at all to his shown output
So like, probably not legit imo, High 6-C was him at the peak of his powers with the ring, Heart of Darkness arc, while does imply him to be him at his peak mentally, actually at one instance seems to imply its nowhere comparable to him at his peak, considering he doesn't fight that version of himself at all, instead letting it falter on its own.