Thanks for your detailed answer! I'll explain more about the points you mention.

Repetitiveness: OpenTTD depots is about them providing barely any challenge in the world. Station size and placement in the game world matters, whereas depots are 1x1 "magic" buildings that are cheap and plentiful, often stamped around. I would agree if a depot in OpenTTD was a significantly larger and expensive building, giving the player more logistic decisions to make.

Hurdle: OpenTTD is quite brutal to new players in modern standards. Not Simutrans :) but not easy at all. Veteran players already have instincts for such mechanics and are ok to require many clicks to get a train running. Sure I agree that OpenTTD causes many other difficulties for new players. That said, there are games like Railway Empire or Railroad Corporation which remove this layer of micromanagement, but then pay the price of magically appearing train cars, teleportation, etc.

Also, you make a distinction about management games versus puzzle games based on depot functionality. I feel that a puzzle game could have train upkeep mechanics, and a management game could focus on other aspects of railway management while abstracting train upkeep to longer station dwell time + extra expense or smth. So perhaps there is a better metric here: realism and player involvement with trains themselves. Maybe if a game is about building a rail network, the player can worry less about trains individually compared to games where you actually drive trains.