Incorrect. Dlss is a hardware graphics layer and is not implemented more than calling an api.

Tech do many other things in a studio

Including gameplay coding, render engineer, etc. In small studios one engineer can do everything.

Att big studios, you still don't have someone working only with render apis for the engine because you have an engine team, most often not in your own studio. If it is in your studio that team is also not only working on render api calls

Hope this explains it to you, you can stop guessing how it works. I know better yes because I am those people. You forget you are the one guessing