When flying with an elytra you are able to gain extra momentum if you angle your flight path correctly, and you can increase your y value as much as you want
Video showing bug - https://youtu.be/oRQBpM1adls

In the video I was able to increase the apex of my flight each time. Starting at 177, then increasing to 179, and finally 184

It doesn't make sense for you to be able to gain practically infinite momentum with an elytra, and it should be more like java where you can only get back to the same y level