hmm, interesting question.
we did gf/cf before we did any "proper" ABA (I say it that way, as all the backward chaining, reinforcement, asks broken into tiny steps was what I did anyway with dd1, and how she ever learnt anything - I wa sobviously not as efficient as an ABA programme, though 
)
gf/cf gave dd the ability ot concentrate. she was switched off, stimming and mostly unaware of other people's presence except to use them as tools. you have met her - her sociability only came about as a result of gf/cf - the absoute joy she gets form talking (quite often gibberish ) to people - the desire to communicate for communication's sake, rather than the imperious demands-of-necessity.
she was unfocussed and dreamy - in another world completely (you know the theory, right? the addiction/high stuff?)
we could have done ABA with her in that state, but it would have been a longer, harder slog, without a doubt.
gf/cf allowed her to have the space ot learn. ABA taught her.
the % split has changed over time, I think. initially, she was os hyper-sensitive to so many different htings (perfumes, soaps, washing powder etc, as well as the dietary things) that cutting everythign right back (only neutral soap, no perfumes anywhere, only neutral soap-free washing up liquid - I even changed the dishwasher tablets! all one step at a time, and all double-tested, and she was reacting to it all. she used ot scream at bathtime - was a water-refuser. we stopped with the soothing chammomile/lavender bubble baths, and shampoos, etc - she stoped screaming. it wasn't the water (although she wasn't keen!) it was all the smells, and the itch of it on her skin.) so at that point, it would have been like 80% diet, and 20% ABA - the diet was everything in getting her to the stage where she could attend/focus/learn (it still needed ot be shaped up - she was an ants in your pants girl!)
but that has changed ove ritme - she doens't react as severely anymore. we still use neutral soap-free for bathtimes, but I can use normal dishwasher tabs, and can use PErsil again.
and when we travel, it no longer matters that she has a different cereal. or the week we spent in Disney - fantastic gf food eveywhere, but way more processed and preserved than she has at home (we are a pretty organic, lentil weavery household). even last year, this woudl have had an effect on her. this year, she did get a bit giggly if she had a sugar overload (eg too much maple syrup on her waffles), but bowel health was ok.
and, she has needed the ABA for control issues all along. now, she can tolerate a bit of goat's milk if cooked (I make her pancakes with it), and the odd bit of apple (previously fruit of the devil behaviour wise). so now, the percentages are reversed, probably - she needs the ABA more than she needs complete rigorous strict diet. but she does still need diet control.