Your preferred appellation for the Sailors?

[Rika-Chicchi]

How on Earth does Sailor Soldier not "make sense"...?

Not a native speaker, but I think it's either "sailor" or "soldier," not "sailor soldier" nor "soldier sailor."

 

[redneonglow]

How on Earth does Sailor Soldier not "make sense"...?

Two nouns.

 

[Seen2]

Sailor Soldier since it's alliterative and rolls off the tongue perfectly. Plus it has two syllables like "senshi."
It works story wise, too. Several adaptations bring up how they're not your typical soldiers. I think Haruka said something like "call us 'knights' instead" in one of the Stars musicals.

 

[ChampionOfNuggets]

Two nouns.

So just like Sailor Scout? And Sailor Warrior? And Sailor Guardian?

Your argument makes no sense.

 

[Memento]

You can put two nouns together... Nouns are often used as adjectives, as is the case with the Sailor part of Sailor Soldier.

 

[Mercurylover]

Anything but Sailor Scouts for me. It just bothers me. Haha

 

[onesurvive]

Anything but Sailor Scouts for me. It just bothers me. Haha

Same.