Which fighter had single best MMA grappling perfomance by "ragdolling" other fighter? Level of opposition obviously matters!
Some examples:
Chimaev vs Usman, Robert
Merab vs Cejudo, Yan
Jones vs DC 1, Glover, Bader, Sonnen, Rampage
Khabib vs RDA, Dustin
Usman vs Woodley
Cain vs JDS 2,3
Islam vs Oliveira
GSP vs Hadry, Fitch, Hughes
DC vs Barnett, Hendo
To review your list:
Chimaev vs. Whittaker is better for me than Usman because Usman survived and in third round Chimaev just kind of controlled him.
Merab vs. Cejudo is better for me than Yan because Yan wasn't controlled or hit with much GnP while Cejudo got carried like a baby across the cage and actually beat-up on the ground.
Jones vs. Sonnen is more complete "rag-dolling" since took him down repeatedly and finished with GnP from your list (Vera and Matyushenko are also elite Jones grappling performances); against Bader he subbed Bader off a bad shot, against Rampage he broke him down with kicks at length before the takedown/back-take/RNC, against Glover it was mostly mauling him in the clinch, and against DC in first fight he got takedowns without much GnP or control. I personally think the Matyushenko one was the most dominant, immediately took down, passed guard, crucifix, elbows to finish with almost no resistance.
Khabib vs. Dustin is better for me than RDA because Khabib did a lot more control + GnP against Dustin and ultimately subbed him (though he did hit some super-sick Judo throws on RDA that were high-impact).
Usman vs. Woodley is very dominant but a lot of the work was done in the clinch (hurt Woodley with an elbow), was able to get takedowns and control with some decent GnP later in fight.
Cain vs. JDS 2/3 is more clinch-mauling than rag-dolling - even the finish in third fight is off a counter to JDS attempting a ninja choke while completely beat-up and getting spiked on his face from Cain escape.
Islam vs. Oliviera isn't really rag-dolling, just Islam getting some good trips/dropping Oliviera, he didn't' land much GnP and the finish came off a punching knockdown to arm-triangle transition.
GSP vs. Hardy is better for me than Fitch/Hughes because GSP got so many takedowns with so much control/submission attempts/GNP; against Fitch he really beat him up on the feet more-so than the ground and Hughes was pretty declined when they fought, also beat him with striking and finished on ground based on head-kick.
DC vs. Hendo is better for me than Barnett; though got great slam against Barnett he didn't get much ground mauling in, more control, while against Hendo he threw him around the cage like child and finished him like one as well with RNC while flattened out.
Out of all the fights you listed I think my favorite/most-dominant ones would be:
Merab/Cejudo
Jones/Sonne
Khabib/Dustin
DC/Hendo
The most complete domination is probably DC vs. Hendo but to be fair that is a HW vs. a MW as is Jones/Sonnen; for Merab/Cejudo it was Merab that got taken down and controlled for the first round.
So based on size/age/athleticism parity Khabib vs. Dustin is probably the most complete "mauling" performance with all things being relatively equal.