Regarding Baselight, again...usability of the feature depends on the implementation of the feature, not just the feature itself. Zooming in on the portion of the curve can be counter productive due to: ....
You need to look at Baselight before making these kind of comments. The curve is presented in a "full size" display, and next to it is a "magnified" view of the currently selected curve point. In other words, it's already exactly what you're describing.
Regarding "single parameter", depends on what is the priority. For example, affecting local contrast by shaping a gamma curve can also be more productive or creative in some cases. If used properly and within its limitations. What curves also do is offer intuitive and informative visual feedback about picture alterations, which may help freeing visual memory and mental processes, compared to trackballs, knobs and numerical values. This is generally speaking of course, and excluding individual preferences and developed habits.
I was asked if I, or other experienced colorists, generally use curves. My answer was and is no, regardless of the reasons that those who do use them make that choice.
Overlaying curves (and qualifiers for that matter) on top of scopes would be a major step up in many factors.
Assimilate Scratch allows that, at least on top of a histogram. Personally, I always found it more visually confusing than helpful.