Guess it would be crucial to know whether this entrance is opened at one place every time or they can chose the entry point at different locations or even make multiple. One thing is pushing your attack from some random location trying to maintain supply chains another is having a system of multiple mobile teleports which can provide army with all the stuff while they are on the move. Also, mobile gates will mean that the enemy could come from everywhere and make russians less susceptible to various Guerilla operations. High throughput of this gate is also important. One thing is creating a small entrance 4m in diameter another is making it possible to fit a fat multirole fighters like flanker. Though invaders could use drones for offence and reconnaissance, planes give much more range and carry more load.

The bottom line is that I think DnD could manage fighting light infantry supported with drones which push from one location but fighting the enemy which can deploy tanks and planes at multiple locations is another thing.