That is not a simple question to answer, the market is not simple to understand.
For example, "call of duty" is a fairly expensive game, which requires an Activision account and many people are not going to play it, but they would play a historical FPS if it were cheaper or without DRM or the need for an account, etc.
Simcity was the reference city builder many years ago, but it made bad decisions that many people (including myself) did not share and I stopped buying them. When skylines came out, despite being very similar, those details were decisive, I have never bought a new Simcity since skylines came out.
These are just examples of how small details alter how a person sees a game.
It is true that many players think that games like "call of duty" are the best war FPS, but they forget that this is not true for everyone, there are other niches of player that will play a war FPS if it offers something different For example, a lower price, not having DRM, even a certain aesthetic, mixing genres, etc.
Normally finding these types of details is complex, you must resort to market studies, something that is out of the reach of an independent developer.
Ask the next question.
Why are you programming a WW2 FPS?
If the answer is because you want to learn or you have fun doing it, then you are not interested in competing with "call of duty", your goal is to achieve a good game.
Maybe you would like a WW2 FPS that has a lot of real story and interaction with NPCs. You will never be able to compete with Call of Duty, but you will find other players who share your vision and enjoy your game.
If you want to make a game that is popular and sells many copies, then before programming a single line, you should do studies and look for information on how to compete with the other similar games.