Even tho I am a noob(Only 835 rating atm, but thats kinda due to not playing enough ranked games as well ) I think removing the teleport from sACU's is the way to go. They would still be decent in combat like the other sACU's just not able to move over the whole map every 10 or so seconds. I have gotten sniped by sACU's a few times myself already, the ones I can remember:
(This one was kinda my own fault in several ways)2 aeon sACU's teleporting right on top of my SMD and killing it simply by damaging it with their guns and exploding next to it. And they came from the other of the map(IIRC setons) with their endless range teleport.
And 2 times getting my ACU killed by 3 sera sACU's teleporting right next to it. They got teleport+shield+nano repair IIRC. Making it extremely durable even against T2 defenses unless you are right next to a spam of them.
I would suggest giving the seraphim a resource upgrade instead on that arm and the aeon already has good upgrades.