I understand the sentiment, but I don't think it's right to think of speed (or stamina) as you would aim, accuracy, or reading since it doesn't really interact with them in the same way they interact with each other. That is to say, speed is generally as simple as turning a knob; all your motions are foundationally identical, you just do them a bit faster.
The other three skills aren't so straightforward in how they interact with each other. Aim is the reliability of your muscle memory to hit an arbitrary location on the screen with your cursor, but without proper reading you won't know where that location is, and without proper hand synchronization you won't click while your cursor is over the note. Accuracy is your ability to synchronize your tapping hand with musical time (hand synchronization is a derivation of this), but again, that ability means nothing if you don't know when and where to click. Reading is your ability to translate osu!'s visual information into muscle movements, but ... etc.
What is speed, then? You could make an argument for speed representing raw movement potential, but I think you'd have a hell of a time explaining and justifying so slippery a concept, so I'd posit that speed is just the ability to do all three of the other skills faster, and that should make the divide fairly obvious. It's both the most fundamental and least fundamental skill.
EDIT: Before we start delving into what is and isn't fundamental and how the various skills interact, it's worth mentioning that aim, accuracy, speed, and reading aren't even foundational; they're the result of interactions between much more basic motor skills like muscle memory, muscle control, hand independence, etc., which can also be broken down further. A huge number of simplifications are made on this topic for the sake of casual conversation, and it doesn't help that the new difficulty calculations throw these sorts of words around despite using them in very different contexts than this sort of discussion would. So... tread with care.