I'm sure Techies is being held back not because of balance  but simply because Icefrog don't want matches going too long.

The nightmare scenery here is a team picking Techies on a best of five and having every match going 90 minutes or more, which fuck up schedule and rise costs across the board.

And since most people hate Techies anyway not having him is no big loss. I believe if he is added back he may lose his stalling potential, perhaps with mines having a far shorter duration on the map or a limit of how many you can have out.