I'm currently playing with ACOT and ME2. ME2 overrides many ACOT features as it comes to ground combat but not all. Combat Drone Swarms and it's base line armored tank like unit. Neither cost Armaments. I had a thought ME could do something similar in which there would be "old style units" which do not require the new type of "arms". Kinda like how we have some 'Flag units' in the modern world which are on horses, or crews and old boats. Except these would be conventional modern tanks, automatic fire infantry, and weak drone swarms. Give the OG military units low morale so they flee intentionally but are still there. The tanks should just have an alloy cost and upkeep. None of these units would get upgrades when most of the rest become upgraded, but they can keep some upgrades which happen (those in which you can't exclude them). This way they are generally a fun RP item and an example of how powerful your sci-fi tech military is becoming. Yet, with some upgrades still happening, a small power move to send three Honor Guard units take over a pre-ftl planet.

Still yet, if you are desperate enough and maxed out on Arms you can supplement (the upkeep shouldn't be better, just different, in fact the equivalent exchange should be less so they are only useful in a surge.