... You can't solve a mechanical problem in the fiction. Any solution would have to be mechanical.
Yes, you can. There will always be issues the rules and mechanics don't cover, that's one of the primary jobs of the GM.
Really. Please do go ahead and explain your non-mechanical suggestion for resolving this.
Let's get something out of the way; fiction and mechanics are not diametrically opposed, they're married to each other. It's not role playing if mechanics don't pertain to the fiction, and it's not a game if the fiction has no mechanics. So, I can agree that "any solution would have to be mechanical," but I take issue with the assertion that the
narrative can't solve the problem.
Second, I thought Xenon pretty much had the best solution
to this problem in particular with utilizing the "ready weapon" action.
But since you're asking, let me show you what I would do;
It's simple. Bring out the disadvantages of their equipment. Put them in a spot and use ad-hoc modifiers.
Examples:
Sure, the elevator's tall enough for your sniper rifle to fit, but not wide enough. When the door opens, and the firefight starts, your weapon won't be ready, and you can't close the elevator doors until the rifle is out of the way again.
Everyone's jumping rooftops? You still lugging that 5 foot sniper rifle and trying to run with it? It's banging into the backs of your knees as you run and puts you off balance for your jump. +1 Threshold on your acrobatics test, and if you glitch you land on your rifle, badly.
You're clearing the room? The hallway you're in is pretty narrow. You can enter but you're operating at some bad angles with that long barrel, you won't be able to bring the weapon to bear this phase at the oblique angles... you sure you don't want to draw your Predator?
The ganger isn't expecting you to shoot him, but that sniper rifle weighs ten kilos. There's no way you're gonna bring it to bear on him before he gets a chance to react. Roll initiative.I'd recommend Dungeon World for further reading. It's quite good, and has entirely narrative gameplay.