There's a perfectly good workaround for the lack of hardware-accelerated video rendering. Just right-click on the video and choose "Pop Out." That launches the video in a pop-up window, which is sized (by default) to the video's native size. You can drag the sides of that window to fill the whole screen, and the video will play at full frame rate.
I tested it with this video:
Right-clicking on it selecting "Show Video Info" gives me "software video rendering, accelerated video decoding." Setting the resolution to 720p and playing it gives me a frame rate of 30fps with no dropped frames. If I use the "Full Screen" button at the bottom right, then the frame rate drops to 19fps (again, with no dropped frames). HOWEVER, if I instead pop it out and then drag the resulting pop-out window to almost fill the screen, then it plays at 30fps while filling as much of the screen as I want it to.