> That's why parallel fifths are considered a bad thing. They disappear into the rest of the texture and you lose one stream of independent movement.
An instrument sounding at the partial a compound perfect fifth (fifth plus octave) above another voice's fundamental can certainly disappear into the timbral texture. But that's quite different from an instrument sounding a simple perfect fifth above another instrument.
Check out the famous parallel fifths at the beginning of Rondes printanières from Rite of Spring. That's strings and winds articulating pitches which are a perfect fifth apart. Simple perfect fifths moving in parallel like that in the bass of the orchestra (or, really, in any range of the piano) are conspicuous and stand out.
It's unlikely that parallel fifths were prohibited during common practice period both because compound ones would accidentally blend into the sounding harmonic series of the other voice, and because simple ones stick out when compared to thirds or sixths.
Moreover, parallel fifths don't stick out any more than, say, parallel fourths. But parallel fourths had long been standardized in practice and theory as part of fauxbourdon.
I can just imagine Satie playing fauxbourdon with fifths-- because, why not?-- and a teacher telling him it's wrong and therefore not to do it. And then we get Vexations, and Debussy, Mahler, Ravel, Polenc, Stravinsky and many others thumbing their noses at the prohibition, creating a new allowance for them that persists into modern film scores even without the initial irony of those composers.