Interesting discussion.
I get that you are sincere in this position, or at least sincerely advancing the argument, but with respect the above is just a restatement of the OP.
For what it's worth I think it's more accurate to define "sandbox", freeform", "open-world" or any other such concept of gameplay by what it does not include.
Mass Effect, for example, is about as far away from a "sandbox" as you can get. Same goes for SWTOR or any other game that is essentially a directed adventure. However the more that restrictive play-by-rails activity is excluded in favour of providing a structure that can be manipulated by the players as and when they choose the more open the gameplay becomes, by definition.
We need to consider the simplest of games to get a sense of what freedom of play is all about. Noughts and crosses is a sandbox game - just an incredibly simple and limited one. Snakes and ladders is not - it's a directed adventure that relies on chance and no skill. Chess, go and bridge are elegant sandbox games, whereas many if not most complex board games are not.
Extrapolating from that basic division (choice and skill vs pre-determination and luck), Elite Dangerous can fairly be described as a sandboxy sort of game, as can a host of other computer games. Many straddle the divide as well - Fallout 3 has many freeform and non-mandatory elements to it, but in the end it has a storyline that must be followed so it not a sandbox game, even though it feels "open" and unrestricted when you play it.
The fact that a game may not cater for a given player controlled mechanic or variable has nothing to do with how sandboxy it is, but with how complex it is. What I hear you saying is that you find ED to be unnecessarily limited at the present time with regard to the scope of possible player activities, but that criticism, whilst entirely valid, is not sufficient to disqualify it from being a "sandbox" or to allow evaluation of its degree of "sandboxyness" - it only defines its degree of complexity.
If you look at the list of games and features you listed the significant thing is that they all share two common elements: open world and no physical limitations. In other words the fact that ED is set within an enormous game world, does not contain a storyline that must be followed to a conclusion, and has no restriction on choice of activity at any time is sufficient to establish it as a sandbox-type game.
just let me make stuff like ships and weapons and operate stations, set the tax rate, make rules and regulations about what is tradable and not, etc.
