How come other streamers get better quality with worse internet/hardware than I and they're not partners as well?
Most likely they're only running at 30fps, which means more bits-per-pixel density. The more frames you stuff down the pipe, the fewer bits there are to describe each one. There's no way you'll get worse-looking image quality at 30fps at the same bitrate, as compared to 60fps. It WILL be better at half the framerate. You also appear to have stuck in a few custom x264 settings for some reason.
It's also possible that they may be playing at native-resolution. Downscaling (full frame or squashing a source down) will always harm image quality to one degree or another. If you're willing to play at 720p, set your OBS base resolution to 720p, resize all of your art assets to suit 720p, your stream will look significantly better. But it will look pretty bad on your screen while playing (unless you have a 1440p monitor, which will just map each pixel to four actual pixels, and look fairly decent).
So, a few potential reasons.