With the new patch on the 19th of November and the (much needed) buff to T3 mobile AA, I think we now have a good opportunity to differentiate SAMs and T3 mobile AA.
First, some history. Obviously, T3 mobile AA was not in the developer version of FAF, but it was added because it was needed. The first iteration of T3 mobile AA was minimalist in order to not change balance very much: It was essentially an exact copy of the SAM, just mobile. However, obviously that was underpowered, so it was eventually buffed.
Now, T3 mobile AA is a low-cost deterrent to T3 bombers and gunships, and a minor threat to passing ASFs and scouts. This is a great spot for T3 mobile AA. Now what about SAMs?
SAMs should be heavy anti-air. I'm proposing an increase in cost by 100% (800 mass/8k Energy --> 1600 mass/16k Energy) paired with an increase in damage (+100%), a decrease in rate of fire (~40% decrease) and an increase in maximum range (+50%), and a minimum range (of maybe 30 units). (UEF SAM example: 200 damage --> 400 damage. Range: 0-60 --> 30-90. Firecycle: 6x1/0.1 sec + 3.1 sec reload = 3.6 total --> 6x1/0.1 sec + 6.6 sec reload = 7.1 sec total.)
With these changes, SAMs will be significantly distinguished from T3 mobile AA, with T3 mobile AA being clearly better sometimes, particularly against masses of T1 and T2 air units and in the early T3 air stage. Also, SAMs that are built alone or closely together will be vulnerable to T2 gunship and will need mobile T3 mobile AA or flak to cover them up close. Also, this will buff SAMs against T3 air, mainly enabling them to One-Shot ASF, and improving performance against experimental air units.