Okay, I managed to fix it. It ended up being a compatibility issue with another plugin, which I could solve by asking the Plugin Author if I could edit it slightly, now everything works immaculately.
Just to follow up what you asked: The string worked after updating the CGMZ Core and the compatibility issue with the plugin also effected the string, so just nothing happened at first in the Console, which confused me.
You can't see it in the Screenshot (because the buttons are too sensitive, so it puts out the same button multiple times) but I tried all of them and every button of the gamepad is put out as true, so that's perfect.
I just want to thank you for the help and quick response, and I am sorry if I have wasted your time in any way. But thank you for all of your amazing Plugins, and all the work you put in them, they are amazing, and maybe this thread can still help someone! (hopefully)