I don't think it's a universally bad thing, but it is something that should be done with some tact. Redrawing something to show the original artist how it can be improved. Fixing anatomy, perspective, et cetera. It's extremely valuable insight from someone who knows what they're doing personally directed towards the amateur's own work instead of a tutorial or exercise.
The issue can be that doing it outside of a critical context comes across as an insecure person flexing their talent in a way that is directed at the other person. A better artist could interpret the same subject and develop an image all on their own, but they're redoing an amateur's work entirely, which doesn't have much of a purpose other that to put themselves up on a pedestal as a better artist and devalue the amateur, as if it wasn't obvious that the original work was by an amateur. There is, or I guess WAS a thread on kiwifarms where it was pretty much just circlejerking redrawing bad art from tumblr and getting legitimately angry at the artists for drawing. That's the sort of thing that feels kind of shitty to me at least.
That's not to say that a total redo of the original image will always be bad, but it feels pointless if it's not being used to educate the amateur about what they can improve upon.
Keeping on topic, this guy is the last person who needs a paywall and I have no idea why he keeps it up. Are there actually enough people buying access to it? Only thing I can think of is he's trying to hide his shit because it's almost loli and he worries about what other people will think.