Make military nodes great again *DISCLAIMER*

Capture the flag would make it a much closer aproximation to leadership/coordination ability.

1v1 arena would practically demand 1v1 balance or have total leadership rotations occur frequently. Additionally without 1v1 balance its more likely guilds have an edge in 1v1 arena tournaments too.
Capture the flag has an easier barrier to entry, and can be designed to make balance less of an issue. Additionally you just need supporters rather than super high level/high skilled people. A shrewd upstart with good leadership ability but no large guild could still make it.

And I'll repeat another suggestion I said somewhere else. Why not both and link it to a communities racial bias. Its an opportunity for race to have a cultural leaning expressed in game mechanic beyond buildings. Capture the flag for some races, 1v1 for races with 'honor' traditions, 3v3 for others. Compromises all around.

Oh, are we having arguments over the meaning of military type civilizations and what type of rulerships historically technologically advance under them? Cuz damn that is up my alley.

I suppose though it'd be more prudent to ask you what your definition of a 'brutal society' is before I go making assumptions. My understanding of a Military Node is that it does two main things: Bounty Hunting and Reduced Corruption timer. These are two 'competing' benefits.

The main example of what I think you could mean by 'brutal society' is Pirates. I can totally see a pirate like 'society' giving both those benefits. I also assume a 'pirate' model is what you mean by brutal societies given you brought up the brute vs strategist division commonly found in the captain vs quartermaster dynamic. However there are many many cases even in pirates where it was not so cut and dry and it was usually a much more cooperative effort in terms of strategy. I won't pigeonhole you into 'just pirates' obviously, civilizations are more complex than that, but they still contain a good model and historical examples.