I very much doubt any flat campaign was (and especially now) is about adding to his legacy – which will always be about his hurdling, which has also taken its hits given the way that career ended up after starting out on such a high.
If he had not been competitive and trailed in last by a wide margin then yes retirement should have been the way to go because it would not be worth doing it at that level and getting comprehensively beaten.
He has very little mileage on his clock at 9 and if he is enjoying being in training and racing then why not continue on with him and if his level is at Heritage Handicaps, Listed or G3 level then there are plenty of opportunities around for him.