Every fountain drink machine uses "actual syrup". They're all mixed in the machine in real time. But yes, many places fuck up the ratio and don't bother correcting it, and don't check it regularly.

McDonalds routinely checks the ratio. They also use an amount of syrup such that if some (all?) of the ice melts, you still have full strength soda. So it's extra flavor before any ice melts. I don't have a citation for that, but a friend once posted a citation explaining it, and I read it. Seems legit. McDonalds Diet Coke has more flavor that a can of Diet Coke, even.