The command element in the compose file behaves strange

Docker Engine General
2

The command property specifies the parameters to be entered after the entrypoint
The child image inherits the entrypoint from the parent image and does not write over it

If you want no entrypoint, simply specify it empty in the compose file

services:
  run-after:
    image: child:0.0.1
    entrypoint: ""
    command: ["/do-something-else.sh"]
    # OR
    entrypoint: ["/do-something-else.sh"]
    ...