Non-Calender Grand Slam is an overrated achievement to begin with.
One of the things that makes the Calender Grand Slam so special is the time frame and pressure it has to be achieved in. There is no break.
Non-Calender year grand slam, you have a whole off-season to rest and recuperate to try and complete it. Yeah, you still need to be a great player to do it, but achieving it in a single unbroken season is far more significant. The "Serena Slam" is overrated for the same reason, though it got more publicity than the Nole Slam.
This point has me thinking about whether the order of the non-calendar slam matters at all. There are obviously three "ways" to win a non-calendar slam, with one recent instance of each:
RG -> WIM -> USO -> AO (Serena Slam 1)
WIM -> USO -> AO -> RG (Nole Slam)
USO -> AO -> RG -> WIM (Serena Slam 2)
I'm inclined to say that both Serena Slams are more impressive (on their face, at least) because she won 3 in a row in a calendar year both times. Winning two slams, then having a full offseason to recover -- physically and mentally -- then proceeding to win two more, isn't quite as impressive to me, though it's still obviously a special, historically significant accomplishment.
As an aside, I think one of the main reasons Serena Slam 1 got more publicity than the Nole Slam is that it came during that pre-Federer period where women's tennis was, quite frankly,
far more interesting than men's tennis. The entire tennis world was attentive to Serena (and Venus) in a way that it wasn't to Djokovic in 2015/16 -- despite his dominance. Serena Slam 2 also got less publicity than Serena Slam 1 for some of the same reasons.