Is cornstarch a less effective thickener when used with gelatin?
Cornstarch can be a bit temperamental.  You can weaken the strength if you cook it too long and it doesn’t do well if you reheat it.  If you use a lot, it could weep.  There is a much better alternative.  ARROWROOT! (not to be used with dairy products)  Arrowroot doesn’t cloud your gravy, doesn't alter the flavor like cornstarch can.  For me, it's just a better thickener.  I use it all the time in my pot-roast gravy that has tons of gelatin and a spot of vinegar. It doesn’t interfere with the silky texture you are seeking.