When and when not to use tty in Docker Remote API
I will respond my own question with everything that I know so far, in case someone sees this.
TTY basically will make the output "look" as it looks in a terminal. That is, if there are multiple folders (in my case), they should be displayed in two different lines.
I still do not know why I cannot see stderr with TTY disabled, but this is the reason I cannot see the full stdout with TTY enabled.