A schematic draws a wire as a line with no properties. That abstraction holds beautifully for DC and falls apart on the edges — the few nanoseconds after a driver switches, when the wire is not a connection but a component, with inductance, capacitance, a characteristic impedance and a finite speed. For most of the time your signal is idle and the abstraction is fine. For the small fraction of time when it is changing, the wire is the circuit.
SPI is a shift register with a wire between two halves of it. That is the whole protocol, and holding it in mind explains everything the peripheral does. The controller has eight bits, the target has eight bits, and the clock the controller generates walks them past each other in a ring: the controller's MSB goes out on MOSI and into the target's LSB position, the target's MSB goes out on MISO and into the controller's. After eight clocks the two registers have swapped contents. There is no addressing, no acknowledgement, no error detection and no notion of a transaction — every one of those has to be built on top by whatever protocol the target's datasheet defines.
A logic analyzer and an oscilloscope look like they answer the same question — "what happened on this wire" — and firmware engineers who own one tend to reach for it for everything, because a protocol decode is easier to read than a wobbly trace. They are not the same instrument. A logic analyzer's front end does one thing: at every sample instant, compare the voltage to a threshold and emit a 0 or a 1. Everything about how the signal got to that voltage — how fast, how far past it, whether it wobbled on the way — is discarded before the decoder ever sees a bit. An oscilloscope keeps that information. It is not a better logic analyzer; it answers a different class of question, and it is the only instrument in this folder that can.