Many Core Commanders will speed up the Sumos by dropping them off near your base. Again, because of the Sumo's hindering speeds, they make an excellent target for Berthas. A few hits from a Bertha should shred any group of oncoming Sumos. Don't forget Merls either. Their firepower does ok damage against Sumos and if you keep them out of range, can ruin a Sumos day pretty quickly.
Lugers work the same too.
The cheapest, and most effective way to handle ground-attacking Sumo's is to stagger Dragon's Teeth all around your base. The Sumo's speed and turning rate is so slow that they will have a hell of a time making it through the maze, and your Guardians will have an even easier time ripping them to peices. Contact us for more information on GameSpy Industries.