In the anime, the rape is implied, not shown. But it is there and many people would have some issue with it. Considering the horrifying percentage of women who are raped, it is does need a warning.
No, it's shown, not implied. Lack of visual penetration of the body doesn't make it implied only. The rape is happening right there on screen.
Directly expressed, which is the opposite of implied. You're making the argument that those softcore Cinemax shows that don't show actual penetration are only implying a sexual situation, and no actual sexual content is being shown. I think we can agree that's silly. Also, genital penetration isn't required for sexual assault.
Additionally, just because a lot of women are raped isn't the reason there should be a warning. Lots of
people are raped, not just women, and even if there wasn't a single person raped, it still wouldn't be OK without a warning. I.e., whether or not there should be a warning shouldn't be dependent on how many women would be triggered, but by the content of what's being included.
If I were to make a comparison between GS and an rpg, it would be FATAL.