What you think is irrelevant, show Cyrax being immune to gun fire, better yet show him being immune to a power staff blast, or explosives, or getting a sword in the face. Here let me save you some time, you won't be able to because he hasn't shown anything to suggest this level of durability, other than the fact that he's a Cyborg.
And let me toss that back at you- Show me something that indicates Slade is immune to Cyrax's giant sawblades, or bombs, or being immobilized by his energy net. Here's a hint- you won't be able to, because he's not.
Cyrax, being, y'know, *metal*, is going to be tougher than flesh. He's not immune to everything, but it's an edge, and he's a very, very skilled fighter with a ton of weapons of his own.
Again, you're acting as if MK characters are unskilled bricks totally reliant on strength and toughness alone, rather than fighters who do superhuman things and fight superhuman foes all days. It's silly.
They are top martial artist by MK standards, not by DC standards., Top tier martial artist hit Batman all the time, you've yet to prove that MK characters are top tier martial artist by DC standards.
You've yet to prove they're less, and we've got zip reason to believe so.
You've also yet to prove that DC top tier is higher than MK top tier, if you want to go that route.
Obviously, there's no way to 'prove' how the tiers compare given the fact that they're separate universe not counting non-canon crossovers- so yea, nice argument on your part, 'I'm going to insist that unless something that can't be proven is proven, I'm just going to assume the one I don't like is weaker'- but take Shang Tsung. He fought and killed the greatest warriors of Earth every generation for 9 generations (once every 50 years). And gained their power in the process.
And additionally I'll note it doesn't actually take top-tier people to hit Batman. Some no-named martial arts students of the unarmed master were able to do so when Shiva was testing his recovery post-back healing. Two-Face is able to do so. Yadda yadda. Lotta people can hit Batman.
Insisting that the very best in the world from a universe that revolves around martial arts are significantly less skilled based on no indication of lower level is, well, a very weak argument indeed!
The only person here who may potentially cause Slade annoyance is Scorpion and considering that he's been beaten by people who are weaker, slower and less skilled than Slade he isn't going to last long either.
Weaker, slower, and less skilled based on.... oh, nothing! And Slade's been beaten by people weaker and slower than him too.
And Scorpion isn't the strongest MK fighter on the list even, not even close.
Long story short of this argument- You're insisting that MK fighters are slow and unskilled based on nothing, and simply assuming the DC ones have big, completely undemonstrated edges. Argument based on assumption is not good argument.