The idea is: If you're disabling weapons for 60 seconds, isn't that the same as repairing the damage you WOULD have taken?
But you don't control the target its shooting at, you do control what gets healed. Also keep in mind the only thing that does 20 DPS or so is heavy cruisers, but that's before shield mitigation and armor. Hull restore reduces the DPS values AFTER that, so for purely defensive purposes keeping repair bots online is better than demobotting a heavy cruiser. Of course repair bots don't stack, while demobots can keep affecting different targets.
The key thing about when to use demobots is not DPS but fleet supply. Hoshikos cost 4 fleet supply. Flak do as well, but in a 1 on 1 battle, your Hoshikos won't beat the flaks before running out of antimatter. Heavy Cruisers cost at least 10 fleet supply, so you can use a much smaller fleet of hoshikos to disable the heavy cruisers, using the remainder for LRF or bombers to take them out.
Demobots can still be used effectively in other situations though, in which you can use both repair and demo bots. If you have all culture and antimatter upgrades, or just an Dunov using its ultimate ability, your antimatter situation will be a lot better, so you might be able to have them use both for a while.
