It's not, it's just too narrow, while Prosperity is so flexible. It's a bit like the problem with Honor in Civ5, but larger, because the tree is so much deeper: it's a great tree when you're at war. It's a bit of a dead investment when you're not.
If it had more virtues like Adaptive Sciences, it would be a great tree but at the moment, it just - overall - cannot compete with the flexibility and always useful bonuses of Prosperity.
Even it's at war bonuses aren't really impressive.
+50% XP from Combat in a game where experience is weak and maxes out at rank 2. Weak, but I don't expect much from an opener virtue.
+15% Production when building Units and +10% per upgrade. Won't help you at all on the battlefield, but it could be useful in the unlikely scenario that you need to funnel all production into the Miltiary late-game for an extended period of time.
+50% of each Strategic Resource. Decent, essentially means a few extra affinity units or buildings.
The only thing that really directly affects combat is a 20% Strength boost.
That is decent, but it's not really worth completing an entire Virtue tree.
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This is how I would change Might.
(Other trees would also receive some buffs, mostly targeted at filler virtues.)
I was actually working on modding it in, but I had difficulties with a perks grant buildings tool that I still need to figure out.
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Survivalism now grants Energy equal to 10x the Strength of slain enemies.
Scavenging now grants three times the Science from cleared nests and Science equal to five times Alien combat strength.
Military Industrial Complex now grants 4 Production in the Capital.
Liberation Army now grants Culture equal to 10x the Strength of all enemies killed.
Adaptive Sciences absorbs Martial Mediation's 1 free Affinity Level bonus.
Martial Mediations now grants Gold and Culture equal to 5x the Strength of all enemies killed.
Army Engineering Corps now grants +4 Production from strategic resources. The energy boost is transfered to Brutal Efficiency.
Brutal Efficiency now grants +4 Energy from strategic resources.
Joint Operations now grants +2 Science from trade routes with Stations per Station tier.