Dominators, Cans, and Morties make going T2 Kbot with Core all the worth while. Arm has very little in the way of fire support or versatility as core in the Kbot arena. Tanks on the other hand, Arm at least still has a chance.
not dead end, just no access to mobile fusion, and no light and cheap units like spiders. Good for powerful mid game strategic strikes, or supporting a large t1 bot army though.