Well first of all we are talking about C41 negative films, specifically Portra, not trannies/slides, and actually the standard does have a very specific relationship to the film curve. That relationship has a "safety factor" built in at the shadow end.

All the manufacturers use the same standard. The beauty of this is that we dont have to test every film to get good results.

The wild card is "us", not the films. Each of us has different expectations and ways of working.

Using negative films, setting exposure with an incident meter at box speed, and developing them by-the-book, IMO provides the most reliable way to get high-quality, easily workable negatives, bar none.

I'm not suggesting that there aren't good reasons to shoot at something other than box speed, or for using spot meters, I'm simply saying that using non-standard settings and reference points should be reserved for "special effects" or "special situations".