Playing on 720p is unplayable, text is unreadable due to how pixelated everything is. It is definitely not actually rendering the game at 720p but something much lower. But, to fix this, all you have to do is force the game to run in 1080p from the steam menu and toggle the switch to use that resolution for the integrated display as well. You might still have to set the game to 1080p in the game settings, but after that the resolution is fine and text is readable. Kind of a shame you have to waste performance by running the game in a higher resolution than your display though