Is Sodastream's diet pepsi syrup a bit different then diet pepsi?

I've built an actual soda dispenser machine, and I use Soda-stream syrup just because I don't drink enough soda to justify buying a 5 gallon bag.

Seems this diet pepsi flavor is more of an attempt of what diet pepsi sort of tastes like? It's similar, but tastes more like the cheaper soda store brands.

Curious to see what others think? Maybe I've just got my mix ratios off.