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Under normal conditions fire breaks (bulldozed areas) work pretty well. We have actually seen a lot of evidence of this here in the San Diego County area even under bad conditions. Unfortunately, the strong Santa Ana winds (that blow from the east out to the west) can "carry" the fire (through burning embers) a long ways- we saw this back in 2003 when the fire jumped a ten lane freeway. The winds also swirl into a funnel that carry the fire unpredictably- even if you have a fire retardant roof the embers can get into the eaves and insulation of a structure.
This time of the year in So. California you have very hot and dry conditions combined with unpredictable strong winds- the elements for a perfect firestorm.

They would and will once the wind dies down. When you have fire jumps 1/4 -1/2 mile from the head of the fire it is hard to put a line in.

Dozers are used to clear trees and brush downwind of a fire so that the fire can’t spread in that direction.

Embers fly in the direction of the wind…. So, clearing any fuel in that direction should slow (or hopefully stop) the advance of the fire…

They are doing just that in Ramona, but there are risks. They run on flammable fuel so they have to be very careful when they send them into active fire areas. We have a bulldozed fire road that encircles our canyon and sometimes the fire literally jumps the fire roads. Flying embers carry the flames sometimes for great distances whether there is a fire block or not, depending on the winds.

the fire is moving at astonishing speeds,these winds can move the fire faster than a car can drive