Mayhaps the Legacy's problem is that it's in one of the most competitive segments, but does a few things wrong for the one thing it does right (i.e. AWD).
In the competitive mid-size segment, fuel economy and value become key - so where you can get a Camry Hybrid that sips fuel by the thimble with 200hp, the gulping 256hp Legacy 3.6R loses its value, especially at $34,695 (a $7k premium over the Camry Hybrid). Not saying everyone should by a Camry, but I think the Legacy's demographic is concerned about value and cost - both initial and long-term.
As much as I love the smooth 3.6 H6, the EJ25 turbo was a better performer all around and typically had better fuel economy too despite being mated to the 4EAT. Add 2 cylinders to the FA architecture and I'm sure that H6 would be a stellar beast, even mated to a CVT
.