True, all works are derivative. But not all works are derivative of something that is still in copyright.
In practice there's little difference. Everything created while your parents are alive will be in copyright until after you are dead.
For this reason, at least in some countries, subtitles are NOT considered derivative works.
Which countries might those be?
The road to ruin is always in good repair, and the travellers pay the expense of it. -- Josh Billings