And they pay for this amount of heatsinks with extremely fragile arms.
That's a property of the asset. I doubt there is a rule in MWLL that says "if you have a lot of heatsinks, you must have fragile arms and are not allowed to mount weapons in your torso" 
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That's actually a property of the vast majority of Clan mechs. Shadowcats, Hellbringers, Summoners, Dire Wolves, Warhawks, even Kit Foxes, Adders, Gargoyles all mount most, if not all of their weaponry in their arms. Contrary to popular belief, the Nova Cat's arms aren't especially vulnerable, they're just laughably oversized and easy targets, much the same way the easiest way to kill a Mad Dog is through a side torso, not because they're particularly fragile, but because they're so massive and easy to hit it becomes a critical weakness of the chassis.
Which means, they are more "vulnerable"... That's how we mean it.
Aaaah Novacat, how do I love thee? Shapely, well-proportioned, canonically accurate and can take the heat.
Indeed
