DBs being dangerous "only in groups" is a position held by the occasional combat-optimised Essence 5 Solaroid Exalt.
To gods? Average terrestrial gods, at that?
Dragonblooded are the Immaculate monks that turn up suddenly when you've just got your region working as you like it, punch you in the face, casually backhand all of your attempts to fight back out of the way, take away all of your shinies and prayer, and force you to do your fucking job again.
Oh, and they can murder you. Gods are used to being immortal. They do not react well to things that can murder them and make it stick. And when the Immaculate Cult has a policy of "if you fight to permanently kill us, we'll fight to permanently kill you... oh, what's that? You mean our Enlightened Mortal monks and Dragonblooded die permanently when you kill them normally, and don't come back like gods do? Well, I guess that's a reason for you to not to resist arrest, then", it makes for rather unpleasant relations as far as those Dragonblooded in the Immaculate Cult go.
More generally, a relatively experienced Dragonblooded who's playing smart can present a serious challenge to even a moderately experienced Solar, especially if the former is combat-focused and the latter is not. And gods, by and large, are not combat-focused. Not even war gods. They're bureaucrats before they're anything else, and while they have Charms that they can use to fight, they're not made to fight with.
However, Terrestrials not in the Immaculate Cult can be recruited. And having Dragonblooded working for you is a sweet, sweet deal. Half-castes and constructs and spirit-blooded and golems and engineered races and Tiger Warriors are all basically "half-price Dragonblooded knock-offs" as far as followers go, you cannot beat the Terrestrial Exaltation for effectiveness as troops, and just one Dragonblood working for a god represents a very powerful piece that god has on the board, with which they stand a much better chance of getting increased amounts of worship, respect and power.
To a god, then, a single Terrestrial Exalt is a combination of serious potential threat, valuable potential asset, and disturbing chaotic factor to account for in their plans. Some will see them as something to be exploited, some will see them as something to be feared, most will see them as something that must be accounted for in any plans or schemes they have going on.
But believe me, a single Terrestrial Exalt is a very, very dangerous and powerful player on the board. It is only next to those of the Celestial and Solaroid tiers that they seem less potent - and "seeming" is never a good thing to base your expectations on. Grouping them together only makes them more deadly and terrifying - they are plenty scary on their own.