FDev threw the cube-square law, and all it implies, out the window years ago. The result is a surrealistic collection of mechanisms that should be mutually exclusive.
Make ships de facto immune to infantry firepower, or make infantry firepower ludicrously powerful compared to massive ship weaponry. The first option would alienate and anger the fresh blood EDO does bring in, while the second will make the fresh blood feel powerful while jading the legacy players.
Ships can be de facto immune to small arms, melee attacks, and even most man-portable weapon systems, without being immune to infantry directed assets. Most bases/outposts have defensive weapon emplacements, for example. The ability to have them target opponents, or even be manually possessed and controlled like an SRV or multi-crew ship turret should be a given. Indeed, this has been a thing in tactical shooters for more than twenty years.
Even a sidewinder has the same mass as a modern tank so there is not a hope in heck a shoulder launched missile is going to dent it, since there is always an arms race of threat vs defence(I.e a missile is developed to blow up X armour, said X armour is upgraded to defeat missile and so on)
A Sidewinder has much more volume, and density decreases rapidly as ship size increases.
There are also shoulder launched missiles that are serious threats to modern MBTs.
But we also have a couple of thousand years of weapons development to consider. My point being, that a shoulder fired Missile launcher should be able to carry a warhead in the same class as a ship launched weapon, just at much lesser ranges.
A ship launched seeker missle is not capable of a one shot kill on a Sidewinder, but is a significant threat. A shoulder launcher missle would/should be a little less damaging, just a lot shorter ranged.
The model for a ship-mounted seeker is about a hundred times the volume of the largest missile that could possibly fit in the infantry rocket launcher we have in EDO.
Ship mounted weapons shouldn't just be longer range, they should be delivering vastly larger payloads capable of at least an order of magnitude more destructive power.