As others have said recent nearby works do not form a precedent in planning terms so just because the neighbour's have large dormers doesn't mean yours should be approved.
What you can do though is use those recent examples to illustrate inconsistencies in the planners interpretation and implementation of their own planning policies. So if they have a policy or guidance document that says rear dormers must be subservient then clearly they have a very inconsistent view on what constitutes subservient. I have seen appeals where that argument has been successful.
What you can do though is use those recent examples to illustrate inconsistencies in the planners interpretation and implementation of their own planning policies. So if they have a policy or guidance document that says rear dormers must be subservient then clearly they have a very inconsistent view on what constitutes subservient. I have seen appeals where that argument has been successful.