The only ground queue for rom marks is Mine Trap. It's pug-able, but don't expect to receive anywhere near max marks for it in a pug. About half the colonists get killed in a typical pug.
If people would stay in their own zone and each pick a building to defend during the initial attack, the mission would be very easy. Unfortunately puggers tend to wander in the preparation phase and you won't necessarily respawn in your own zone if you die, so at least some zones will usually end up being overrun due to lack of defenders.
It's still much more pug-able than ground STFs. At least the clueless players can't ruin the work of others.