A good idea to enhance the Galaxy Legion experience would be legion combat.
A legion would divide into three groups, an Assault Battle-Group, a Defence Battle-Group, and a ship vs ship Fleet.
The Assault Battle-Group would specialize in the attacks on enemy bases, the Defence Battle-Group would stay near the Legion base patrolling and defending against enemy Battle-Groups and the main Fleet would fight against enemy Fleets and occasionally assist the Battle-Groups.

Expand on your idea more.

If I'm reading this right, the idea is to divide the legion to three groups -

*One third of the Legion ONLY to be able to PVP
*One third of the Legion ONLY to be able to attack enemy bases
*And the final third to (somehow, the game doesn't have the mechanic for it) defend your legions base against attackers.

Please correct me if I'm getting this wrong.

Incorrect, the purpose in the legion is Two quarters fight another legions Ship to ship combat fleet, whilst one quarter protects the base and another attacks another base, it's not PVPing, it's a whole new thing, it's effectively a legion war system. All groups can still PVP and NPC, this mode will only deduct energy from the leader who starts the battle.

I had a post about PVP leagues.

This wrestling game i played had a leagues where you would be paired up against someone on the other team and then you would fight it out till you pinned your opponent.

Usually each member had 3 fights and got a 1 point for each win. Team with most points wins the match.