It’s not what’s there, It’s what’s missing

Keep in mind that while I consider myself a scholar of the Martial Arts, I'm far from a historian.

My thought: different arts aren't really defined by what they include, but by "what they take away." To expound on this thought, what is fighting? Hochheim states it's everything from ICBMs, tactical/battlefield nukes, B-57s, gunships and artillery, machine guns, rifles, pistols, clubs, knives, then empty hand. Notice how much there is there? You can further take the subset of combat, empty hand, and include:

Strikes:
head butting
biting
shoulder thrusts
elbows
forearms
open-hand strikes
fists
hip checks
knees
all the various kicks

Grappling:
standing grappling
ground grappling
throws
traps
locks/breaks
takedowns, trips, sweeps, etc.

There's more, you're welcome to add to that list via comments, but the idea is the same. What differentiates styles is what they take away from that list.

Judo, for example, started out as what? Jujitsu. So did Aikido. What differentiates them from their ancestors? What they took away - much of the vicious striking and some of the grappling techniques were refined/modified.

The same is true of every other art, including karate (I always use lower-case to denote the generic Okinawan and Japanese striking arts and their derivatives, including TKD). What's taken away, in general, are many of the items on the lower list of grappling. Not all. Stylistically, some will include more or less than others on each list, but the formula is more or less correct.

Just a thought...