Hiya. I am a level 182 chef on Rhiannon with 1630 mastery. I can confirm that chocolate gelebrons work for me quite well whilst making Bara. I have a theory for this that was created in conjunction with some of the other chefs on my server. This theory is that the exquisite foods have a maximum possible chance to be created, and that, beyond 1800 mastery, the only thing that goes up is the chance to create perfects. This is because the maximum experience level that can be obtained from cooking Bara (without experience degradation) is 180. My best guess is that these "Maximum Exquisite rates" correlate with the "Maximum" experience level of the food. Maximum Exquisite rate seems to be somewhere around 23%.
So you would agree that at 1475 mastery, I should proc just as much as someone with 1800 mastery or higher on a chocolate gelebron? That just isnt the case. Also your theory on maxium exq rate is flawed and disproven simply by my inventory. Leveling my mastery I have cooked 1669 gruel with 575 exq and 72 perf which is a 34.45% rate for exq. If you dont believe me, test it with any other low level food and you will see that your max rate is disproven.