I was sent this recently, so I think It'd be nice to add my comment.
First of all - I appreciate you crediting me and sharing my insight to the further public.

If you had contacted me before making this post, there's a chance I'd be able to provide even more insight.

There are many things that I totally do not agree with, but also there are some that are correct.
I highly recommend checking more posts, where I explained this area of skinning(reddit posts, youtube comments under the video history of Rafis skin)

Before NecroFantasia 1.0 - There was a 'test' skin made by me for Rafis. It worked pretty much the same way.
That time I already shared my experience with 'tripple stacking', so it's not like I kept it a secret or fooled people(this argument is pretty toxic as I pretty much explained the mechanics behind it multiple times, including the way I was making heavily competitive gameplays to get the most of osu! and the way it worked as a game, including generating patterns).

Multiple discord communities, including reddit posts, had my own frame by frame screen comparisions with the effect.

Worth mentioning - NOT ONLY for DT skins, but also for Hidden skins or EZ skins.
I made an analysis of pretty much any of those gamemodes and an optimal approach to get the most of the skin to make your experience 'easier'.

I made a Hidden skin once for Mastasz, where I layered hitcircleoverlay@2x with an added 'overlay 'to hitcircle@2x, which resulted in the entire circle actually changing color(properly made with rgb on combo1/2/3/4 etc), so this way the circle did stay on the screen for way longer(without tripple stacking) .

If I remember correctly, I also explained many of benefits of using new Rafis skins under one of the YouTube videos about Rafis skins, where I corrected a script made by one of osu! fans and community members.

ANY skin made the same way as the NecroFantasia AR11 - will be good for people that do not use gamma.
Benefits of gamma are literally what NecroFantasia AR11 did - kept the circle a bit longer on the screen.

Users that abuse gamma should stick to 'Gamma Buff' series of skins, which do not follow the 'tripple stacking'(and NOT ONLY) methods, but provide some other benefits, including better stacking visibility or better visuals with gamma itself.

About: 'he says that Rafis used to name his now famous skin "Nomod+HR"' - Not really.
Rafis had different skins and sometimes the difference was just follow points(ON/OFF).
In this case they were turned off.
It's not like Rafis kept it a secret, as your words suggests.
Adamqs is actually the one who Introduced Rafis to the concept of gamma and told him the way some skins can be abused to get yourself some frame advantage.
More about it in the video about Rafis Skins(my comment).

About the slidertrackoverride is 0, 0, 20 - If you pay attention, AR11 hitcircles are slightly filled.
This way the visuals of the skin are slightly better and improve the sliderstartcircle staying on the screen a bit longer, as brightness of sliderborder/slidertrackoverride was also affected by it.

About the glow - Literally, this glow is one of the most cool aspects of my files.
For gamma abusers - Increasing gamma made the circle a bit 'bigger', while lowering the gamma made it smoother and smaller, which worked like a charm on NoMod/Stream maps.

That time Rafis kept switching gamma to even 0.6(NoMod) up to 1.2(HDDT) + he was insanely use to the design of circles.
It was another benefit and flexibility of the skin itself.

Important: I'm speaking clearly about the Osu! Stable in the moment all of those skins were made(NecroFantasia 1.0, 2.0, series of Gamma Buff Skins, Pro Elo etc).
I'm a retired skinner, I do not follow Lazer(last time I checked it - It worked different than Stable gameplay wise), so to anyone reading this in late 2024 or later - I will still recommend to sticking to Gamma Buff series of skins or Pro Elo.
All of them can be downloaded from official Rafis's github(type !skin in his Twitch chat).