What, doesn't 13,000 infantry sound epic enough?
Not to mention in the second system a legion fights at full strength until it is annihilated, and 100 centuries can't be combined into a legion...
How about a compromise - make troops small in size and equippable with components such as weapons and armor - say 2 to 10 kT - but call them legions anyway (a legion is 10,000 men right? 10,000 men x 100 kg / man = 1,000,000 kg = 1 kT, and a legion of infantry might carry equipment equal to its mass, while a legion of tanks might be 90% machines and 10% men.) I know it seems weird to have a legion so small, but really, these are PLANETS we're conquering, right? A legion just won't cut it, it's not like we're invading Pottsylvania