It depends on the fire support unit, too. An LRM boat can stay out of sight, avoiding the AC/2, but that means it's adding a minimum +1 To-Hit to do so, and that's only if they have Infantry or another motionless unit with a clear LOS. If they're relying on a VTOL (aside from TAG) or a unit like a Locust, you're looking at Walking or Running AMMs being tacked on. That also means that the Spotter will likely be taking that AC/2 fire. Meanwhile, a Blackjack can be flanking with its Jump Jets to force that LRM Boat out of cover.
A direct fire support unit like the Awesome, Marauder, or GunNerdslinger, has to have the same line of sight the AC/2 has, and aside from the Gauss, the AC/2 is plinking outside of the response range.
With rare exception, there is a use for every tool. That use may not come up often in the scenarios you play (A-Pods, for example), but a good player is only concerned with making the most of what you're stuck with.