The thought occured to me -- since it stands to reason that stereo CD players can't suffer from whatever ill effect it's supposed to be that's said to make stereo carts less than optimal for playing mono LPs -- that if this alleged deficiency in playng mono LPs with stereo carts is true, then on average, mono CDs therefore ought to sound better relative to the their mono LP counterparts than do stereo CDs relative to stereo LPs (for those of us using stereo carts -- most, I'm sure).
This isn't something I've noticed however, not that I've specifically listened for it. (Then again, despite owning more vinyl than "discs" by a factor of over 20 to 1, neither am I one who thinks LP sound is necessarily always better than CD sound. I think mastering quality greatly trumps format, but also that, mastering quality aside, each format can have its strengths relative to the other.)