Now do it on 700 (default gravity)
In all seriousness, though, the main reason i recommend playing this map on 400-500 gravity when running it on a server is because of how hard it is when playing with a higher latency (even 30-40 makes a big difference for the harder jumps). Looking at your video, i think you would have a chance of completing the map on it's intended gravity level, though I'm quite interested to see how your jumping style affects this.
In regards to your map; I think it actually has some potential, though the rocket jumping parts are a bit too much like jumping maps from TF2. If you could keep the style found in the beginning consistent throughout the map, it would defiantly improve the experience and re-playability. That's not to say you need to make everything super detailed, but try and make it seem like a real location and not "oh here's a bunch of squares, jump to the end"; This gives us something to look at along with a feeling of purpose/immersion. Of course, doing this takes a significant amount of effort due to the planning and elaborate setup it takes to disguise some jumps, but it's easily worth it if you're willing to invest the time.
Anyway, if you're designing your map with low gravity in mind, it would defiantly be worth the effort to stick a "trigger_gravity" in the spawn area of the map to reduce the gravity by a percentage for players joining automatically (0.57 is equivalent to about 400 gravity); this would allow the map to run on its intended gravity with the default settings.