OK. First, to clear things up:
FENDER 9050 FLATS ARE NOT, AND I REPEAT NOT, MANUFACTURED BY D'ADDARIO.
The D'addarios flats are chrome; the Fenders are steel.
That out of the way, I was a confirmed roundwound guy for 35+ years, including Roto Swingbass, GHS Boomers & Progressives, etc. I always thought flats were hollow, thunky, etc.
BUT...the new Fender 9050's are different. They have completely switched me from a roundwound guy. I always had trouble with twangy G strings. Not with the 9050's. I always had trouble with inconsistent intonation. Not with the 9050's. I always had trouble with consistency of tone, both up the neck and string-to-string. Not with the 9050's. Many strings are very expensive. Not with the 9050's.
The 9050CL set has it all: tone; growl; consistency, both up the neck and string-to-string; no twang; long life (my current set is 1 1/2 years old and still just as I put them on); feel; economics.
They sound like a cross between a subdued version of Rotosound Swingbass and an EB version of the Spirocores I have on my DB.
At least, try a set. But they are not made by D'addario. They are made by Fender.