The series always had rankings, but it isn't until Armored Core: Master of Arena that you can fight each other. In that game, the lowest-ranking ones, even after the post-story unlockables are very weak. Along came Armored Core 2 and Armored Core 3. In Armored Core 3 and the sequel Silent Line, the arena also features a post-story unlockable enemies. The catch is that the lower in the rank they go, the tougher they are, so much so that in Armored Core 3, there's an email challenging you to defeat the bottom-most opponent, Exile, while giving you the Game-Breaker OP-I (albeit you need to train it properly first) just to give you a slight, repeat, slight edge over the opponent.
Indie Intermission - 'Knightmare Tower' Next Time We Take The Stairs
When Vytai Bloombeck jumped ship to join the Union on Santee, his recruiter didn't bother to check his qualifications, just slotting him into a pipe-cleaning job. When Vytai whined about this, he was assigned an even worse job in the sewers, and a combination of screw-ups, a terrible personality, and a reputation as a petty conman have kept him there ever since. Protagonist Padma Mehta has assumed for years that his prior career was as a low-level gardener, but when she sees him clean-shaven for the first time, she realizes the tattoo on his cheek marks him out as a genetic engineer, and he's a genius with plant diseases.