I've been looking at the wiki, and the formulae for the attack and defense values of certain matched enemies are extremely complex and probably don't actually represent reality. So I took it upon myself to try to rederive some of these formulae based on my and existing data, and it turns out they all have the same form:

Attack or Defense Value = X * Roundtothenearestinteger( ( Y / 10 ) * RANK ) - 50

where X and Y depend on the enemy and whether it's its attack or defense, and RANK is the rank of the enemy / rank of the player facing the enemy.

I've derived the X and Y values for a number of enemies. I'd put them on the wiki, but I don't know how to get permission. Instead, I'm posting them here.

Dark Runner: Attack X = 9, Y = 5; Defense X = 15, Y = 5

Sha'din Charger: Attack X = 9, Y = 4; Defense X = 9, Y = 4

Stryll Assassin: Attack X = 15, Y = 6; Defense X = 15, Y = 6

Rogue Tech Collector: Attack X = 10, Y = 6; Defense X = 15, Y = 6

Dark Trafficker: Attack X = 5, Y = 5; Defense X = 15, Y = 5

Stryll Trapper: Attack X = 10, Y = 6; Defense X = 10, Y = 6

Sha'din Penetrator: Attack X = 10, Y = 6; Defense X = 10, Y = 6

RSL Siege Cannon: Attack X = 25, Y = 6; Defense X = 10, Y = 6

Sha'din Shockfighter: Attack X = 40, Y = 3; Defense X = 10, Y = 6

Lazuli Harrower: Attack X = 20, Y = 6; Defense X = 15, Y = 6

Mylarai Extractor: Attack X = 10, Y = 6; Defense X = 10, Y = 6

Sabre Gunship: Attack X = 14, Y = 6; Defense X = 8, Y = 6

Blade Harvester: Attack X = 14, Y = 6; Defense X = 8, Y = 6

T.O. Troop Carrier: Attack X = 10, Y = 6; Defense X = 10, Y = 6

Dark Arms Carrier: Attack X = 5, Y = 6; Defense X = 25, Y = 6

Rogue LabPod: Attack X = 10, Y = 6; Defense X = 10, Y = 6

Rogue Experimenter: Attack X = 10, Y = 6; Defense X = 10, Y = 6

Dark Iso-Runner: Attack X = 10, Y = 8; Defense X = 30, Y = 8