These are uncommon mechs and longarms are an uncommon weapon which means according to plarium they're supposed to be trash.

Slingshot is literally an exact replica of killshot but trash cause it has much less HP and much worse ability damage. They even gave it the name slingshot to drive home the point that it's a worse killshot.

Why? Well the reason is simple. Pay to win. They put things into distinct quality categories to make it so any brand new idiot spender could easily know what to buy to give them a leg up.

I think it's quite ridiculous. But at least now that lower grade stuff is cheap it could be worth upgrading some of it, if mechs and weapons power ratings reflected their actual grade. But since we don't have real power ratings the only serviceable lower grade stuff that's worth upgrading at all is low energy capacity mechs. Not even because they have appropriate power ratings but because their low energy capacity means weapons don't add as much power if you maxed out the capacity of a higher energy mech.

And if they things realistic power ratings, that would give new players reason to upgrade and use mechs in gear hub tiers 1 to 6