EM, I am not a 'fluff' adict, but as far as I understand it the Marines, Orks and IG are the most generic lists, set loosely in the 40k period (though largely modeled on WWII). The other lists are more specific variants so you may be correct about Seigmasters and Swordwind.
However, as you suggest the real issue is "why do people play?", to which you will get a whole spectrum of answers, and which is really at the heart of the questions you raise. As Neal and other will point out, the whole intention behind the original design philosophy is a bit of light hearted relief or fun, away from the prescriptive rigours of life and summed up by Legion 4 and his phrase "Do What Works For You". Away from more formal competitive settings, the designers actually encourage people to develop their own ideas and styles, which is actually the antithesis of the prescriptive design you are suggesting.
I am not saying you are wrong, quite the opposite. Researching into a series of detailed campaigns and battles can be very enjoyable for some people. But as others (including Morgan Vening) say, given the nature of the GW 'universe' and philosophy, this cannot be the
only approach for E:A.
Have you seen (or preferably bought) the "Raiders" supplement yet? If not, I would strongly recommend checking it out
here. Now imagine a similar supplement for the campaign / army of your choice. Or perhaps you want to provide some lists for an existing piece of literature or battle, such as the "Taros" campaign etc. IMO this is where a more prescriptive list fits in, and in this format it may well encourage newcomers, providing it is couched within the general E:A philosophy and is not intended to direct it.
And with a more sensible (ie something that might actually be out there) list balancing would get easier.
