You get my point regarding the 358, 404, et al., which I see as superior solutions to starting with the pencil, often recommended for beginners. As for Spencerian being solely a shaded hand, I thinks that's nonsense or, at the very least, myopic. Does one really believe P. R. Spencer expected people to write some other hand when forced by circumstances to use a pencil or crayon? What are most 'business' hands if they aren't unshaded Spencer?
Where was I – or anyone here, for that matter – talking about using pencils? My post, which you replied to, concerned only the advice (often given on this forum) to start off by using nibs with limited flexibility, before moving to the truly flexible nibs later on. I have no problem with beginners using rigid nibs or pencils to practise letter forms but do not see the point in telling them to use nibs of limited flexibility when the problem they are encountering (nibs digging in) is largely due to a heavy hand. You seemed to agree with the advice to use less flexible nibs when you wrote "It's [the 358] a safer, less frustrating general purpose point, one I believe better suited to beginners than the most challenging points", so why are you now reframing the issue as one of pencils instead?
As for what constitutes Spencerian script, you may call it nonsense to describe it as a shaded hand, but that is what I have consistently and (to the best of my memory) without exception seen it described as. I cannot recall ever seeing an unshaded exemplar described as Spencerian script, and in the many discussions I have read online, I cannot bring to mind one in which the writer used "Spencerian" to describe an unshaded hand, except for you above. Usually, the shades are highlighted (along with the ovals) as being a defining characteristic of Spencerian writing. Such an example may be found in the Spencerian Key to Practical Penmanship:
"the circumstances in which we present it [the Spencerian System of Practical Penmanship] to the public render it proper that we should briefly allude to some of the features which mark it as peculiarly "Spencerian."
Seventh.—In the shading. The natural as well as artistic distribution of light and shade upon the letters in the Spencerian writing is, indeed, one of its most prominent claims to originality."
As for what Spencer thought, he found beauty in the contrast between the shades and the hairlines, writing that,
"Were all writing executed with heavy downward lines, as in the old-fashioned round hand, it would possess no more beauty than if the lines were uniformly light, since excess of shade as effectually destroys the contrast as its entire omission.
"It is the graceful blending of light and shade which gives light and beauty to the productions of the artist, and renders paintings fountains of delight, from which the eye of the beholder may drink and never weary. And what is writing but the picture-work of thought?"
Seems to me that if he had wanted a script to bear his name, he would have wanted it to be a shaded script.
But I'm open to being convinced that I've just somehow missed all the discussions and exemplars wherein unshaded script was clearly and unambiguously described as Spencerian script, so I would be grateful if you could furnish examples of this usage.