Its better than you think, It just doesn’t have great “out of the box experience”. Some of the settings are coming over from desktop so Quality > Performance (or most tested to have at >30 fps on nexus 5 w/ the power house Snapdragon 800).
Almost all of that 450mb (probably ~350 is just from all the high resolution textures, in all the varieties that android devices need). I have a blank 3D prototype project and it is down to ~80mb… so it is not bad, but it can definitely improve. The engine alone takes up about ~25mb, but this is getting better.
Just like any system, you just pick up on stuff and it make sense but I can guarantee you the epic team is focusing on the out of the box experience (Documentation, Examples/Samples, Easy Config settups, Quality of Life Features, Compatibility). I’ve spoke with some staff members personally and after seeing the iterations showing it, i believe them. I’m sorry its not quite where you would like it to be, if you need any help and let me know and i’ll try my best to help.