The boxes have helped with birds that just won't plant well, when a dog and handler reach that point in the grand the last thing you want is to spend more time than needed looking for a bird that has flushed wild. If a bird is trapped, which isn't too often, the bird planter will dizzy another bird and plant in another area of cover.
I would like to see natural plants and flushes but I truly understand why the use the boxes. The intent is that the bird is walking away from the box when the dog gets into the scent cone and we can watch a natural flush.
At our local hunt we are blessed with very good bird planters from the spaniel world and we always have natural plants without baskets, pop boxes or the boxes, which we don't own any of the latter. We have a bird planter that will follow the judges and handler and if we get traps the bird planters change the way they plant the birds. A bird that is planted too hard or in too heavy a cover will not be able to escape a fast flushing dog and that is what we are testing not a pointing dog, so if they point you better be able to encourage them to move in and engage the bird or you are out.