Recordings have a whole new optimized way of streaming. They are no longer downloading big MP4 files, instead they are streaming the replays in optimized HLS chunks. This means they load faster and are available instantly at 4 different resolutions. The player will automatically optimize the resolutions as the video is being played to maximize the the resolution will minimizing buffering.
Also, if you hover over the replay timeline you will see thumbnails to help you find specific spots in the video.