Why amazon clouddrive is so slow?

i have to cloud storages: google drive and amazon cloud drive.
On both i have exactly the same, 500mb video mp4 file.
When playing from gdrive through rclone mount nginx webdav it starts playing after 5 seconds.
in the same config from amazon it takes more that 30 seconds to start to play.
Tested many times, with different config options while gdrive is default, no modifications.
Tested with templink threshold to 0,
buffer-size from 1M to 128M,
without parameters,

amazon is just very very slow.