> multiplier for some known value of some known quantity

Of course, unless it's a multiplier for an unknown value of a known quantity, like every amplifier, filter, and sensor specified in dB.

> For instance, in the case of loudness of noise to human ears in air, the unit can be taken to be dBA

Unless you're using dBB or dBC, but of course we all know exactly why you'd use dBC (more suitable for figuring out safety of high impulse, short events) or dBB (it's somewhere in between - you'll know it when you see it).

> The apparent excessive complexity is necessary, not invented to create confusion.

Wait, so writing dB instead of dBA is now necessary, not just convenient?