I know you're taking the weapon costs verbatim from Iron Demons but I'd like to suggest some changes. Personally, I'd split melee weapons into 3 categories: one handed, two handed and giant.

-One handed weapons are all melee weapons meant to be used in a single hand like some swords, handaxes, knives and daggers and so on and they all cost a single point. Why would anyone go with a knife when they can get an axe, sword or whatever for that same point, you ask? Because knives are smaller, which means they're easy to conceal within the mech's frame for a surprise backup weapon and they're also easier to handle and more reliable in very close quarters, where larger weapons would be rendered ineffective by the lack of room to set up a proper swing or thrust.

-Two handed weapons would be melee weapons that are still generally within a reasonable size (scaled up to the mechs, obviously) but require two hands to wield, like larger swords, polearms and whatever else people might like. These cost two points, no problem here, right? Bigger means an extra point, but seriously, they're not that large, they're reasonably sized, there's historical precedents.

-Giant weapons are all those ridiculous, Buster Sword sized shit that physics and people who know how weapons work hate to death but fictional works love because they're cool. Sometimes. When people aren't cracking jokes about overcompensation. Anyway, these go for 3 points because they're massive, require more effort to carry around and swing and deal more damage because they really are that large.

And then you do something similar for shields. 1-point shields are smaller round or heater shields that don't cover the whole body, 2-point shields are larger shields that more easily cover the entirety of a mech without having to move it as much and then 3-point shields are the massive tower shields and shit like directional energy shields that basically protect the unit from harm coming at them from whatever direction they're pointed at.