points of note:
. marker bombs do not illuminate the field, they aren't supposed to provide field-visibility. They just provide a visual cue. You bomb the cue.
. the marker bombs blow nothing up. you can tell when your field has been marked, you know it needs capping.
. most marker aircraft were un- or poorly- armed (the un-gunned mosquito being a typical example)
. marker bombs aren't laser guiding, they are a smoke column which stands out to the bombers eye, but onto which the bomber will have to carpet a bit, therefore a marked field is going to need more bombers than a normal field bombing, ergo this contributes extra factors to those of us who enjoy strat and missions - it's also great event/HA stuff.