That’s an interesting journey. It uses an extra train, but cuts off quite a chunk of mileage by avoiding West Hampstead.
You may get lucky on one occasion and get them to allow a refund, but I wouldn’t repeat it until they decide, if they do, to add the alternative route.
To request the alternative routing you can use the help and contact facility on the TfL website. They may well have to consult with SWR and get agreement, so it won’t be a quick process. It would be beneficial to give them as much information as possible, including approximate journey times, to persuade them that it is worth considering.