I wrote the comment assuming buying CDs because that’s how I like to do it (I like having a physical device) and because that also gives you the used option which is often cheaper (although my 10-15 calculations are based entirely on new albums).

But if your needs are entirely digital, buying an online album is even easier than finding it on Spotify, and finding that it’s often not available (because the particular artist hasn’t licensed with Spotify) and/or if it’s even slightly not mainstream, Spotify will bury it under the mainstream options it would like to push.