Lossless Capture with FFmpeg
libx264 is a very efficient encoder, so that bitrate isn't unusual. In fact, it's on the higher side, but since you're capturing a game, I expect there is constant motion involved, and your preset is ultrafast which disables some of the aggressive compression.

When you say 80MB/s, I believe you're thinking of uncompressed full raster i.e. 1280 x 720 x 12 bits/pixel x 60 fps. Lossless does not mean uncompressed, just like there can be a compressed ZIP of a binary program.



BTW, the -framerate 60 goes before -i video="Game Capture 4K60 Pro Video 01" as it's an input option.