In a lot of forums, questions of trade-offs between alternatives come up.
One of the advantages of flavored coffees over syrups is cost per serving. Flavor shots add about 25 cents per serving. That is twice the cost of the coffee.
There are also questions of freshness with syrups. Not all syrups move at the same speed. Though it is not a coffee example, it is illustrative. 20+ years ago when I was in high school working at a Friendly restaurant scooping ice cream, we noticed that nobody under 50 ate maple walnut ice cream. It was OPIC - old people's ice cream. As a result, by the time we got to the bottom of a 6 gallon can, it was pistachio.
If you have a lot of syrups, one of them is going to be pistachio by the time you get to the bottom.
There are different qualities of flavors. Most leave a heavy chemical aftertaste. There are some that don't. This is one of those cases where in general you get what you pay for. Cheap flavors taste cheap.
Even with good flavors, they actually taste better with cream and sugar. The fats in the cream bond with the flavors and spread them out more evenly over your palate - cream and half and half are better than skim from a flavor perspective. Then you need a little sugar to take off whatever chemical flavor there is.
So there are cost trade-offs, freshness and convenience. And yes, never, never, never put regular coffee in an airpot that had a flavored coffee in it. You'll never get enough of the flavor out so that customers won't notice. Better to mark them. P-Touch labels are waterproof and last a very long time - and they don't look cheap.