That seems to be the fallback of literally ever SV player. The only argument is that people never gave it a chance, that it’s unpopular because it has a bad rep, that the peeps hating on it have “never given it a try”.
It’s all BS. It’s literally just presuming something, then taking it as established fact with zero evidence, and then hinging the entire argument on it.
You can believe whatever you want about why SV is unpopular, but without data one way or another, that belief is simply wishful thinking. The data shows that the spec is unpopular, period. You can make claims about why all you want, but the fact is, the spec has never had more than a ~2% representation in any raid tier since it was revamped. It’s high point was 1.34% in BoD. In fact, the only raid tiers it has exceeded 1% raid representation were Uldir and BoD, and both of those it was at ~1.3%.
You can claim undertuning. You can claim bad rep. You can claim that it was never given a chance. But all of those are still just suppositions, literally guesses and wishful thinking, with no data to suggest they are a more likely explanation than the many others that have been put forth.
It’s also worth noting that two of the primary points SV enthusiasts bring up to defend the spec’s poor representation, that it was not given a chance because of how it was introduced (and at what cost), and that it’s melee without a reason to be brought over other melee, are also arguments against it ever having been implemented in the first place!
Seriously, look at the representation chart (link, if you don’t have it handy). No other spec has been as unpopular as SV for that entire period of time, despite near on half the specs in the game having received major reworks in Legion, and several more (and/or again) in BfA. Even Sub, which you point to, was the most popular of the rogue specs in Nighthold, ToS, and near-equal to Outlaw in Uldir before the heavy-handed nerf in 8.1. Heck, even Arcane is making a comeback now, in addition to having superior representation in literally every single raid tier since Legion.
That all said, my bitterness about MSV’s origins aside, I’m not actually advocating for it to be removed (well, usually, depends on my mood). RSV should come back, but it should either come back as a 4th spec for hunters, or SV’s gameplay, as closely as it can be, should be transplanted to a class where it makes more sense, like DH. Change the ability names and animations, but keep the gameplay as close to existing as possible, complete with Mongoose Bite.
Frankly, I’d be fine with either one. Something tells me that moving it to DH is more likely than a fourth spec, if for no other reason than the whining other classes would put forth that they didn’t get a 4th spec too.