You are on the right path but also you are a little off center. In the type of match they grappled in it took away Randy's greatest advantage and biggest asset in wrestling. The takedown.
Remember also in the international wrestling styles exposure is rewarded, not control. It is all about exposing the opponents back in FS/Greco, while holding them there CAN win the match just exposing the back scores. So those styles train to take a man to his feet and towards his back. If you think of a Judo Ippon, this is also the same type of throw or takdown that gets rewarded the most.
This is why you see moves like a leg lace score or gut wrench or gator roll. They dont show control, they simply "expose" the man's back to the mat.
So you take away 2 of Randy's 3 most practiced areas by having rules like you stated, all he has left then is the pin in which case this type of event does not reward him pinning in guard so he has to pass which a wrestler in a wrestling match would not bother doing.
I dont see how this allows Randy to use his strengths. It would have been a MUCH close "mixed style" match had Jacare somehow been forced to stand by rewarding Randy with takedowns points if Jacare conceded the takedown by pulling guard.
Randy was forced to "wrestle" the entire fight in Jacare's element while Jacare was NOT forced to "wrestle" In Randy's.
I dont see how you can make that argument. Especially in a grappling match. In a "fight" or mma bout, ok because of the strikes there would be some way to punish the guy who pulls guard, even if you cannot pass.