In theory, heavier/thicker vinyl is a better playback medium than lighter/thinner vinyl because a heavy/thick record will vibrate less during playback and will deal with heat created during playback more efficiently.
In reality, there are too many variables involved, so that none of the theory really matters. Some of the best-sounding LPs in my collection are thin, flimsy, floppy discs. I have one or two thick "audiophile" LPs that are awful.
Most of the thick "audiophile" records sound good, but it's less to do with the thickness of the vinyl than to the care put into the mastering and manufacturing.
