Actually, aspartame and splenda, when added to a product in the factory, do not contribute maltodextrin. Being hundreds of times as sweet as sugar, MINISCULE amounts (About .05-.1 grams) of these substances are used in a typical MRP.
The maltodextrin content comes in when you get these sweeteners from a small "coffee shop" packet, where the mixture is 95% maltodextrin for filler purposes. They add it, because quite simply, it would be difficult to pour six grains of aspartame out of a packet into your coffee mug.
Again, this "filler" is not added to commercial aspartame-sweetened products, like diet sodas, MRPs, etc.
Oh, and sucralose does not spike insulin. And the nutrition facts for 1 gram of pure aspartame (NOT Equal, or another filler-based brand) are: .96 grams protein, .04 grams ash.
Hope this helps.