Hi Fatparrot,
DynaGROOVE records were lighter than Shaded Dogs, but they were still around 110-120g - reasonable. It was only during the later DynaFLEX era that RCA's records got truly flimsy, under 80g in many cases.
Regarding poor quality vinyl, to be fair I should have said "some" Dynagrooves. Like you I have Dynagrooves which are nicely silent. Others have general background noise that resists all cleaning and which I can only attribute to poor quality vinyl.
That cost-cutting, "they won't hear the difference" mind shift which drove lighter record weights, dynamic compression and frequency balancing for low-volume/low-fidelity playback presumably also drove a move to lower cost materials.
My copy of "Fragile" is also extremely good, and minty too. (Yes, Doug actually owns a rock record. Who knew?!) I wouldn't think of replacing it, but it's great there's a well mastered new release for those who need one.