@IWRATS: I kind of assumed the cow fields along Gilmerton Station Road were green belt until the executive homes started to sprout. No objections from Swanston or bypass-users to my knowledge.
As far as I can see e.g. here it was green belt up until the Edinburgh Green Belt Study in the mid-noughties - though shown as Grade 5 quality (Grade 1 being the highest quality). The cooncil atlas now shows the green belt boundary in that area as being on the south side of Gilmerton Station Road, and kinks further south to avoid the industrial units at the east end of GSR before kicking back NE on t'other side of Gilmerton Road.
This report about the Edinburgh Green Belt Study identifies that area as part of the "Burdiehouse farmland" and states:
There is limited capacity for residential development on the shallow south east facing slopes above Burdiehouse village, and west of the A701, and also on the north west facing slopes above Burdiehouse Burn, and north of Loanhead.
Development has certainly gone ahead in the two areas identified in that statement, but there's nothing in there about the Limekilns development on the other side of the A701 at Burdiehouse, or the Gilmerton Station Road one,or the one to the north of the Lang Loan - all of which occupy land which was previously shown as green belt but isn't any more.
Remember, though, that from 2011 the "safe pair of hands" in Westminster (one blue, one orange amber) declared a "presumption in favour of sustainable development". I can't recall whether Scotland had, at the time, the option to take a different path. I do recall that no-one could find out what "sustainable" was supposed to mean in that context (there was a strong suspicion in certain quarters that all it really meant was "profitable"). AFAICS the issue has been before various courts a number of times without a useful clarification being forthcoming.