Companies need to use proper throttling/rate limiting, block ports used for updates, and make it useless for people hammering it, so that it's useful for all. Otherwise, what happens is what you experienced. I suspect the difference between usable and non usable onboard WiFi is due to different equipment being used to provide it.It's not just whether it is free but how usable it is. I was on a transport for Wales service at Wrexham. It gave first 20mb then throttled back. My phone synced some mails and used that before I left the station. It was unusable after that.
For on the move WiFi to internet, 250 to 500kbps is sufficient for browsing, music, mail, etc. That 20mbps you got could have served 30 to 40 simultaneous users before anyone found it unusable, if it was preserved to be used that way.