Yeah, Borderless Window is nice in some cases; but it really does hamper performance in a lot of them as well. I have a sneaking suspicion Borderless Window might be what’s wreaking havoc on framerates for some people with lower end GPUs.
You cannot say this game was designed for PC in mind when you’re lacking basic options in the settings menu. You do not design a game with PC in mind with console features like variable resolution being a default option, required for the recommended specs to actually perform proper.