I'm not "equating it" as such .... I don't use Spotify myself but I have seen many, many comments about it being poorer quality, low res / lossy / not as good as CD over the last year so and was questioning how bad it is and if it was worth having a decent HiFi if that was the primary source.
Indeed, your question is totally reasonable, people do say that at lot on forums. But rarely do they mention how they compared or how big the difference was.
FWIW, I do have a "£10K system" and I find the lossy/lossless (or Spotify vs lossless service) differences, whilst real, are exaggerated by most people and/or there are other reasons for the observed difference in sound quality than purely the audio codec. For example, different mastering, different playback apps in the OS, wrong Spotify quality setting, bad streaming setup vs good CD player, expectation bias in sighted test etc etc.
But that's audiophila I suppose!