"...which ruined the Sentry's servos. Naturally, it couldn't aim, so when it detected enemies it would just fire in a straight line. The bullets made a hole in the walls, and eventually the floor, which is why this wiring is sticking through at such a random location."
Matter to explain what is that supposed to be?
Aand we now have all the players (who have made their forms) in the game, big whoop.
The Detonator's flare did hit the Pyro, but not much damage was done to him due to resistance to fire (and your Axtinguisher being worthless). The Pyro on the other hand pulled out his shotgun and started to open fire at you, which is much more effective than your flares.
The sentry goes up quickly, but the enemy Pyro is outside its range, despite being on the corner.
As you come out of the hallway you notice a friendly Pyro rush at another enemy Pyro with his shotgun out around the right corner, and you can briefly see him waving his hand, which you easily interpret as "Follow me."
While you rush into the empty room with your comrades, you quickly start capturing it with great success, and the Engineer begins to make a nest with his dispenser and sentry. The Soldier points and the door in the other end of the room and commands you "Go, go, go, charge!" while he pulls out his dreaded rocket launcher.
RED is not behind, as they quickly capture two rooms, with the Medic and Heavy temporarily splitting to accelerate the process. They do not know that their newly-acquired "bases" are far from each other and require much walking to get to.
FYI, the combat system here is more DF-like than TF2-like. (and yet Mediguns work like in TF2, but still, think Meet the Medic.)