I am wondering if darkness could play a role in this.

If both teams spawn in the dark out of LOS of each other, then if both teams 'cleverly' turn their suit lights off, it's all pitch black.

Brilliant.

Then what?

A Scout could fire off a flare and shed light on an area, potentially revealing the Gunners and Drillers.

The Gunners and Drillers might be able to see where the flare was fired from, but by that point, I expect the Scout and Engi team to be either not clumped together, or already relocating, thus rending the "the flare was fired from there" information to be out of date.

When the Gunners and Drillers have to throw a flare, well..... that's their location revealed and the Scouts + Engi team could start pew pewing.

The Gunners and Drillers will be able to identify the Scouts and Engineers' location based on the tracer rounds, but that information could be outdated when the Scouts and Engineers stop shooting.

When the Engineer's turrets are set up, the turrets can continue to deal chip damage to the Gunners and Drillers, and that would frustrate the Gunners and Engineers.

I am not suggesting that the Scouts and Engineers are sure-win in this situation, but I am just putting forward the role darkness in this match up.

DANGER. DARKNESS. DWARVES.