Your hypothetical scenario is unbelievably insulting and offensive to the millions of women who would love to live in that reality rather than the real-life scenarios of sexual harassment, rape, discrimination, inequality, and gender bias that they are CURRENTLY going through and have endured since the dawn of time. Really, I want you to know right now I take your statement seriously, and I want you to know, bluntly and clearly, that I find it derogatory and offensive.
But to answer your question, in a hypothetical scenario of equality where everyone gets equal and fair treatment, having a game that exclusively starred men wouldn't be inherently sexist, but if said game was like FFXV, where the women are beaten and exist only as peripherals to support the men, be rescued, and are "strong" only to make the men greater, then it would still be sexist.
You act like sexism doesn't also factor in men. While men tend to have it better in our world, there is an unhealthy sexism of machismo in many parts of the world, where men are expected to conform to the standards of being strong and masculine and shamed for enjoying or experiencing more "feminine" feelings or experiences. "You throw/hit/run like a girl" is still an insult culture tells men to avoid. Many gay men all over the world face this stigma to this very day. Even straight men who are just quiet, shy, or gentle can and have faced ridicule, and this is also unhealthy.
So, yes, your scenario would still be sexist, and I'll again state your argument to disregard all the sexism we currently face is just as offensive to me as asking me to disregard all the racism or xenophobia or homophobia minorities face.