When devices were a bit larger, we would customarily refer to “boat-anchors”

That was a pejorative for unwieldy and inconvenient devices like rugged government secure cell phones that lagged behind consumer tech.

Brick means entirely useless except as a doorstop, projectile, or building material.

I beg to differ. "Boat anchor" not only has the connotation of uselessness, but is also well-documented, such as in the official Jargon File by Eric S. Raymond:

http://www.catb.org/jargon/html/B/boat-anchor.html

1. Like doorstop but more severe; implies that the offending hardware is irreversibly dead or useless. “That was a working motherboard once. One lightning strike later, instant boat anchor!”

I contend that brick is a neologism based on this boat-anchor analogy. A brick is rather small, handheld, portable. No computer component was this way when the "boat-anchor" term was coined.

Indeed, many of my colleagues in the 90s based their trust and confidence in hardware on its volume and mass. If we could lift it, or throw it across the room, it was not worthy of respect. Those were the days of magnificent racks loaded with equipment that did comparatively very little!

This was the prevailing definition in California/Silicon Valley 20 years ago.

You're a different person with a different perspective obviously.