They really aren’t. Combo points chi hp all work the same way you use X ability to gain Y amount to use Z ability.
Runes in the other hand are gained passively or though a few select talents or ability’s depending on what iteration of the dk your on. Then there’s how runes we’re in the past with blood unholy frost and death where you could mix and match your rune use for different abilities giving you an amount of choice that combo points have never had.
Hell with the logic you are using you might as well Say rage is combo points as you need X amount to do Y or else you can’t do it or it’s less effective.