They shouldn't worry about the footbridge or the main bridge after the cave door is destroyed. Just check the aiscript and you can see that I turn off all those actions:
action 39 // tunnel door explode action
{
// connect the nodes
node_connect 176 367 true
node_connect 195 368 true
// make sure everything is turned off
deactivateAction_Group 1
deactivateAction_Group 2
deactivateAction_Group 3
deactivateAction_Group 4
deactivateAction_Group 5
deactivateAction_Group 6
deactivateAction_Group 7
deactivateAction 0 // main bridge construct
deactivateAction 1 // axis cp
deactivateAction 2 // tower construct
deactivateAction 3 // footbridge construct
kill_action 14 // tower mg42
kill_action 37 // footbridge satchel action
// move to the next phase
activateAction_Group 8 // axis aggressive
activateAction_Group 9 // axis conservative
activateAction_Group 10 // allies actions
// activate the allied cp
activateAction 79
}
As for the grating, the allies do use it sometimes. The focus is getting the tank to destroy the cave door though.
If you are finding it too easy to win as Axis, turn up the bot skill and aim skill. Sometimes even when played by all humans, the allies never make it past the tunnel. So unless it's happening 100% of the time, I think it's ok.
EDIT: Updates have been made. Check this
thread