I am thinking give it a Disruptor with a low RoF. This would require Moderators to keep the slow damage from decaying between shots, and the removal of the riot role would mean that using Firewalkers to screen against raiders and anti-heavies becomes a positive synergy. The Sumo would then be good against light assaults from ravager to reaper, as well as being anti-heavy in combination with moderators (which firewalkers suck at). Slow damage from Sumo and Moderator ensures the enemy stays in the fireball as long as possible and cannot close on the Firewalkers, while the slow allows the Sumo to retreat easily through the wall of fire, being one of the best retreat-repair heavies in the game this increases that focus.
The issue with it being anti-heavyis that the Jack and Skuttle are already excellent anti-heavy (though actually not great vs Ravager). If you want to field Firewalkers though, you cannot use the Skuttle. They have negative synergy.
The thing is, since the jump-bomb ability, which is 'cool' and 'unique', it's been somewhere between the Jack and the Firewalker.
The Firewalker has the AoE to take out the kind of light unit balls the Sumo is good against. The Jack has the HP and mobility to assault, walk through fire and jump right on top of enemies like the Sumo.
The heat-ray is a non-starter. It melts every kind of heavy at close range as well as being good vs raiders: and the jump makes closing range trivial + adds AoE vs raiders. You cannot have a riot/assault/anti-heavy.
Anyway, I really want a factories late-game comp to have positive synergy. Scythe/Sniper for example is phenomenal and just 'feels' right for the fac. The shieldball is the ultimate synergy death machine, focusing on the brute force and HP sharing of the factory.
The sumo was just 'spam sumos'. This sucked.
