Or the ~11k pages long ARM specification.

That's actually two specs in one, both ARM64 and ARM32 are part of this.

If I remember correctly, the entirety of the original GSM is ~9000 pages, things just got crazier (by orders of magnitude) from there.

That's comparing apples to oranges, though. Those standards also specify the interaction between network components, not just between your phone and the network.

Mobile phone standards are more like the entire RFC collection than like the 802.11 specifications.

Things are far more complicated these days vs the 90s. These specifications still seem to lack important details which you notice if you try implementing the spec.

You don't need to implement the full spec. Most devices only support the parts relevant to them. Hardware in general is very expensive though so I doubt a very long spec that helps you achieve comparability with existing devices is the thing holding you back.