It's just not the same without Stance Change.
In STABmons, the most common users of KS are Heatran and Ferrothorn, who both use it defensively. Setting up SR or Leech Seed happen all the time without KS in play, so I don't know why you're complaining about that, and Heatran and Ferrothorn are not going to win the game because they got those moves in "for free." I've actually found KS to be a liability in a lot of scenarios because of the free turns it can grant for the opponent, as many people know Tran/Ferro often have it, and can re-use Fake Out, Swords Dance, use Earthquake, etc to burn your turn, thus making it a riskier play for the KS user. It also fails to do anything against a Defiant mon such as Braviary. Do I attack it with Blue Flare or risk a Superpower / Swords Dance? These are questions you have to ask yourself when facing any setup mon in STABmons, as attacking on the turn you think the target will setup is often the best option instead of switching or using KS, and for Pokemon without KS, the 50/50 is still relevant.
You could probably compare a more offensive Steel like Mega Scizor to Aegislash, which can use KS drops to buy extra turns to setup Swords Dance, but it really likes having Roost + coverage. Offensive Heatran uses the move to combo with Doom Desire, but considering DD's timer, there are two possible turns when the Heatran will KS, giving the opponent time to react accordingly (which is where Roar comes into play).
The Sucker Punch + Pursuit combo, in my opinion, is worse, as there are more offensive Dark-types that can capitalize on the 50/50. Tyranitar with Dragon Dance, Bisharp and Weavile with Swords Dance, and Crawdaunt with either setup move come to mind. They're all more likely to win you the game due to a misprediction than the Steel-types above, but they've never been the cause for concern, mainly because PixiSpeed and FakeSpeed (the latter bar versus Tyranitar and a healthy Bisharp) exist to keep them in check.
tl;dr - It's riskier for the KS user because the misplay can cost them the match, whereas the setup mon will usually just take a chunk of damage. There are no sweepers with KS and no Pokemon that can abuse Stance Change. Defensive Heatran and Ferrothorn don't win games with it.
It's also kinda one of those "cheap" strategies everyone complains about when they first start playing STABmons, similar to how Transform Chansey and Prankster Spore are annoying until you learn how to play around them. Counterplays to consider are Substitute and Taunt, making yourself "imposterproof" (a bit harder to do in STABmons), switching to a Grass-type/Magic Bouncer, bringing a Defiant mon, attacking with a special attacker, etc etc.