And still does not deflect the reason why some will say that the chashash of kitniyos applies. Obviously there are differences if kitniyos should be extended to include, but for that ask your own Rov, if you have one.
the OU and the Star K both allow Quinoa. In fact the OU did a complete investigation into Quiona and even went down to Ecuador and saw exactly how it is cultivated. You can read about it in the OU magazine they had an entire article last year or 2 years ago (I think, but it was very recent)
Anyone can assur anything, It takes a Talmid Chacham to actually mutar something.
There really isnt much differnece between Cake and Bread. There is a differnence but its not huge. Potato Starch cake and cookies is very common, you can make a bread in a similar way