I agree completely. I've just had to book a very complicated home to work 1 to work 2 to home trip and it took ages and I still don't have the flexibility I might need, so may end up binning off one set of tickets and buying afresh.
It occurred to me that rather than advances being for a specific service, they ought to be for any service except specific ones, so rather than being quota led, the price point is determined by how restricted the passenger is prepared to be
No question advances are good value, but the specific service thing is awkward.