Dragons make perfect sense as minions in any setting in which player character power makes it logical for a player to be able to drop a dragon in one hit.So why do dragons not make sense as minions, but giants do? The whole point that the dragon example was making was that giants don't make sense as minions, to them.
And dragons would make sense as minions in a "War of the Lance"-style setting, so I don't see how it's some absurd example.
I guess its up to you to decide whether there is any level at which any published character class could plausibly down any published dragon in one hit.