I have re-read the definition several times and I don’t get why some people say that there can only be one Omega mutant per power. The way I read it, this is just a list of mutants whose power is limitless. Both Jean and Quentin’s telepathy is limitless, therefore both are on the list. It is not a competition of whose power is the strongest in each power category.
I think it is the example with Magneto and Forge that confuses people. The whole ”Both Magneto and Forge are the most powerful mutants of their power types ...”. But that is not the definition. The definition is: ”A mutant whose dominant power is deemed to register -- or reach -- an undefinable upper limit of that power's specific classification.” And that means that if several people with the same power set have no upper limit to their power they will all be omega. The reason why Emma, Betsy and other telepaths are not here is not because Jean and Quentin have taken their spot, it is because their power has an upper limit.
This is not a ”there can be only one”-competition. It is just a list of mutants who have no upper limit to their power.