You're right but most of the house buying activity in ED was speculative waiting for the ELL to go through. By time the actual line was finalised the area had already started to establish itself. Ed also benefitted from good state schools Heber and Goodrich and also being less than a mile away from the fee paying scholls of Dulwich Village.

You can still get into London Bridge in 12 minutes and in a TFL zonal sense Ed is closer in and riplle effect etc will dictate that given a certain amount of factors the closer areas gentrify first and then the overspill starts to benefit the surrounding areas. I think that a lot of people are now starting to see HOP and FH as a far better alternative to ED. I certainly did.