[TDM is] not meant to be a de facto training ground for Skirmish or a Skirmish simulator -because TDM is its own beast and it plays out invariably different from Skirmish.
Unless your location doesn't allow you to feasibly access one of the Skirmish servers, I'd suggest simply queuing up for Skirmish if you want to practice Skirmish.
A small point before going back on topic, skirmish/captain is not an optimal mode to practice fundamentals. TDM is much better suited, due to high likelihood of getting a fight and fast respawn times. Skirmish/captain mode is where the fundamentals are applied. Game sense, teamwork, etc. is what is practiced. TDM is very fun and super necessary as its own game mode for sure.