Hm, i like that deployable Archelon ability idea. Nanoswarm mines could be really cool, or maybe a "nova" of nanobots similar to Epsilon Adept's deploy ability. It'd probably have to leave the vehicle disabled for a few seconds; maybe that's when it could get temporary mind control immunity?
Either way, it seems that we have a solid consensus that the Archelon needs some love. Everything else is so badass and then you have the dinky Archelon. Looking at the role of stolen tech units, a pattern is very clear- they're mostly anti-unit with mild effectiveness vs. infantry armor, generally ineffective vs. structures, and then you have the specialists like Grumbler and Archelon. Archelon's offensive ability is limited completely to clumps of infantry, using its stealth to get in range and take shots. That alone wasn't enough for a stolen tech unit, so I think they made it an infantry healer in hopes of making it more unique and competitive with other stolen units, but it just comes up short. Compare it to the Sickle, which shares the inability to attack buildings, but has a personal Iron Curtain, super fast, and a weapon that annihilates infantry in groups (a lot like Morales' sniper rifle) as well as quickly frying lighter-medium vehicles, even performing well against heavy vehicles in numbers.
I kind of thought the Foehn's stolen Epsilon tech would be a combo of nano tech + gravity tech, rather than nano+stealth. Foehn isn't a stealthy faction, so it's kind of out of place. Imagine something like... an Athena Cannon platform, but instead of calling down Mercury strikes it fires down magnetic bursts like the support power. Damages/immobilizes vehicles for a few seconds, good vs. buildings, doesn't affect infantry unless they can be EMP'ed (Knightframes, Tesla Troopers, etc.) and is very fragile. Has a deploy ability which disables for several seconds after generating a nanobot cloud which slowly heals any Foehn that enter and damages enemy infantry that touch it. Something like this is balanced with weaknesses and the power we expect from stolen tech, the versatility needs to come at a steep price. It'll probably just remain a stinker that goes relatively unused, unfortunately.