Craigmillar had the population of Mussleburgh
Perhaps in numerical terms. Both are on the edge of Edinburgh. There the similarities end.
Musselburgh is a historical port, has a large stake in the establishment (Loretto school, Brunton theatre, QMU campus, race course, etc.), and has much better transport connections with other settlements (including a rail station). It's also administratively separate from Edinburgh, being the largest population centre in East Lothian.
So to compare Musselburgh with Craigmillar is not fair on the latter.