It is a scam. It should absolutely be assumed that you
could perform these job functions - it makes you a way better engineer! But being
expected to is a scam because the skill ceiling on each is so amazingly high that only a scam artist would expect someone to be able to perform all three to a specialist level. The same issue happened when QA departments got the boot. I deeply understand testing strategies (both manual and automated) but this is an important enough job that it deserves a dedicated person. Not having this person is exclusively because the business is trying to save money and make the worker easily replaceable.
It is not better for the department members or the software itself. It is only good for the bottom line. Yes, if you know it all you'll be valued higher - but the company is still reaping the majority of that benefit from you and not rewarding you with 3 salaries. You should not perform all the roles because it's economically idiotic to do so. You could contract out all 3 services and make a shit ton more money than you would performing them in a salaried position.
That is a scam.