I have to confess that I don´t know how it is operated irl, so anything I will say is based on wild guesses.
You are right in pointing out that crossings are operated by external buttons. Like the one you can find in Juliusz. But in this case, the dispatcher has a direct view on the crossing. No CCTV needed. In Slawków you cannot see crossings in plain sight so for the sake of the security a CCTV is needed. Having the chance of opening/closing them from the monitor is an added feature as to speed things up, not a real thing. The best scenario would´ve been having the CCTV active in front of the panel to double check for traffic but operating the crossing through the panel. So far, I am afraid is not possible as when roaming in the room the CCTV monitor is not active.
Any working solution? Maybe adding buttons on the panel so they can be operated through buttons AND/OR CCTV. It would be up to the player to follow the best role.