I, on the other hand, could say something is more neutral and something else is less. That's why I said Cockney was less neutral than RP. Isn't it to you?
I'm not going to try to strictly define what I mean by "neutrality"; it's too difficult. But I certainly think that a simple, absolute definition like yours makes the problem too simple. My definition, if I made one, would involve some kind of numerical representation of accents based on statistical data and then would say that the neutral accent is that one which has the highest representation. Of course, what exactly I'd like to represent and how I'd do that requires much thought. The existence and uniqueness of the highest representation should also be considered.