Roundhouse kick. When did Raidude even defeat Shao Kahn before? He got his ass kicked in MK9 & the trailer. Even in MK Annihilation he got destroyed.
Look at the distance he was standing at against Kintaros army. Just look. It was YELLING distance. So I still don't understand why you keep bringing up "he would kill himself" when he didn't. I've already noted this before, and how silly it looked. Once again, MKX "atoms".
And you give Mileena way too much credit, for someone as desperate as her. Kano comes in and says "look I can get rid of Kotal in a blink of an eye, your biggest enemy, there might be some collateral damage if done inside a city". Do you honestly believe she would say "heck no go fight a pseudogod in a 1v1 hand to hand combat!"??
I dunno man. Seems like the ultimate means to an end.
He still dodges it and teleports Shao Kahn right after. Good god, I'm not saying Raiden has to defeat him, I'm just posing a hypothetical situation where
literally all he has to do is touch him. It's funny how you think Raiden just touching Shao Kahn is something that could never happen, yet Kano and other characters can pull out these nuclear cannons and take them into every battle.
And okay, Kano is now going to assassinate Kotal Kahn with a nuke. He immediately demands his payment be doubled, because there's no way that tech is cheap even if you think the U.S. military could just hand out one to every soldier. What happens when Mileena doesn't have the money? She believed she already had a secret weapon in Shinnok's amulet too, so she probably wouldn't feel all that excited about coughing up the money for some untrustworthy Earthrealm weapon. In fact, Rain would probably advise against it as well per his own plans, and his own not wanting to possibly get hit by a nuke; after all, their actual plan in the game went awry because Kotal was early, who's to say something similar wouldn't happen? Kano wasn't even supposed to 1v1 Kotal, it was supposed to be a quick and dirty assassination. You might as well ask why Kano didn't just bring along a bunch of Black Dragons to help him kill Kotal, they're just as much a resource as the nuke blaster. Tremor could have totally knocked all of Kotal's forces over, making it easier for Mileena's to slaughter them, right?
Also, how's Kano's supposed to carry this huge-ass cannon into the city without immediately being put into custody by the guards? And if he tried firing from outside the city, there's no guarantee he'd be able to hit Kotal at all given how small the explosion in this chapter was when it only wiped out half of Kintaro's army; you yourself just said he fired it from yelling distance and it didn't even kill all of them, so it's clearly not as powerful as an actual nuclear bomb. So if Kano fired and missed, and that was it (given how it definitely seems these cannons can only fire one shot), he'd still be in a lot of trouble.
I think you're seriously too worked up about this, and you might as well ask why Kano didn't get an actual nuclear bomb and use that to kill Kotal.