You're right that there is evidence in multiple species to suggest that testosterone can enhance existing
aggressive behavior, at least in some cases — meaning we might expect an
intact male dog to have a faster or more intense
aggressive reaction to a given situation
than a neutered one, all things being equal.
For example,
intact males constitute 80 percent of all dogs presented to veterinary behaviorists for what formerly has been described as dominance aggression, are involved in 70 to 76 percent of reported dog bite incidents, and are 2.6 times more likely to bite
than neutered dogs, while unspayed females «attract free - roaming
males, which increases bite risk to people through increased exposure to unfamiliar dogs,» and «contribute to the population of unwanted» and potentially
aggressive dogs (Gershman et al., 1993; Sacks et al., 2000; AVMA, 2001).