Sprinkler design is heavily standardized, and probably to a slightly lesser extent fire alarm design (though I can neither confirm or deny this, as I've never designed a fire alarm system). There are facets of fire protection engineering that rely far more on engineering judgment (egress calculations, alternative solutions to prescriptive compliance, heat release rate and combustibility analysis etc.) than standards.
We don't have NICET certification in Canada, so every sprinkler system design needs to be signed and sealed by a Professional Engineer. Of the 40,000+ professional engineers registered with my Province's engineering association, I might be able to name 10 that could design a sprinkler system. And of those 10, I know maybe 2 that could do a real sprinkler design (that can be cut and pre-fabbed with a slight chance of actually fitting the building). It might seem like I'm embellishing those numbers. I'm not.
Is an engineer still an engineer if he makes his living rubber stamping sprinkler drawings without knowing the difference between a dry pendent and a dry valve? Sure, why not. Thousands of sprinkler designs get done here every year, and every single one has a stamp on them.
Asking idealistic, philosophical questions is sort of a hallmark of a new person in the industry. After 10 or 20 years in this grind, you'll be able to answer your own question. And the answer will probably be something along the lines of 'who cares if I'm considered an 'engineer' or not, as long as the money is right and the work is interesting enough for me to drag myself out of bed year after year'.
I guess what I'm trying to say is, don't sweat job descriptions too much. You chose a great business to be in, and being an engineer or not has very little bearing on how good the money is. Give it 5 or 10 years when half the designers in the business retire and there is no one to replace them. Then we'll really be talking.