[prof1515]

Exactly. Armageddon had many features not found on the other RPIs. Likewise, those games had and have many features not found on Armageddon. The original application of the term did not relate to a single game but to more than one that shared similarities. Citing Armageddon as the "feature type" is creating an identification with one game and its features when those features are not universal to all RPIs. Some of them are, but not all.

For example...

Armageddon features ranged weapons. Ranged weapons were not found in Harshlands.

Armageddon features accounts. Harshlands did not.

etc.

This is the same problem one would face if it were called the Shadows of Isildur feature set. Not all RPIs have literacy code, swim code, hands in place of an inventory, etc. Even while Shadows of Isildur's code is the basis for over three-quarters of the RPIs open or in development right now, it doesn't encompass all of them.

Likewise, how Armageddon achieves some of the similarities common to RPIs is also different.

For example...

Armageddon displays skills without any assessment of aptitude. Harshlands utilized a three (later four) term scale. Both kept precise assessment of skill aptitude vague through though.

Armageddon used account systems to differentiate players. Harshlands (originally) used email addresses alone. Both identified players and limited them to a single character at a time however.

Describing RPIs through the use of "Armageddon feature set" could lead to all of Armageddon's features being considered. As Jazuela pointed out, there's only one game with that set. Likewise, someone who is not familiar with Armageddon would have no greater understanding of what the term meant than if one simply said RPI, though at least with that term they would have the basic motivating philosophy that underlines feature and policy implementation: role-play.