I guess we have to agree to disagree . I think in part that's because the name "shear web" blinds some people to the fact that, as well as operating in shear, these elements of the spar structure also carry (distribute might be a better word) some of the normal tension/compression loads. This they do better as an I-beam (and that's also where the part about fitting between the ribs comes in). It's easy to see why people don't bother though. As you correctly say that structure is much more difficult to build well and really does rely on completely accurate fits everywhere.

I'm relieved that I'm not the only one who recognises the variable loading along the wing though. Many years ago we built FF models with tapered spars and spars that only covered part span out from the root. I can't remember the wings ever failing anywhere but at the root .

Steve