What Kyuss said - (got in before me

)
Basically it is a question of 'balance'. In reality, battles are always fought between uneven forces. However people like to play 'evenly balanced' games to see who is the better general. In this way, Epic games are much more like Chess.
Your suggestion is a bit like asking to add Japanese Chess pieces to a game of Western Chess, played on a Chinese Chess board and possibly with the addition of dice to allow pieces to 'fight' when one piece takes another. While I am sure that it would be possible to do this (and there are a *lot* of variant Chess rules and games out there), doing this only to one side would make the game very uneven and less enjoyable.
In Epic this 'balance' is achieved by a variety of mechanisms in each list, and unfortunately this results in the considerable number of Races and lists out there. Indeed this approach is central to all other miniature rules.
However, what I think you *may* be asking for is a spreadsheet listing the units possible and the army lists that contain them.
This spreadsheet would allow people very quickly to find that Hornets and Lynx are only in the Eldar "Yme Loc" list, or that Marine Bikes are a core choice in the "White Scars" list, and would allow novices to pick the list that most suits the units they would like to use.
Or as Kyuss says, you can always just put the models on the table - just don't complain if this ends up feeling very one-sided . . .
