Okay, so before we begin, let's introduce both our lizards and our metaphor. So, the side-blotched lizard, a desert species found throughout the Southwestern United States, has 3 color morphs, namely a reddish-orange morph, a blue morph, and a yellow morph, each of which have male lizards with different mating strategies.
Then getting further into strategy, there are some fundamental differences in what strategies the teams and lizards use to hold territory, which happen to conveniently parallel each other.
Valor or the reddish-orange lizards get bonuses in gym battles, and thus tend to hold large numbers of gyms and defend them aggressively. Valor (red-orange) lizards hold large territories with large numbers of females which they aggressively defend, essentially holding a private harem. One of their main issues is that the aggression means they compete with each other over females. And yes, I can confirm that Valors do that.
Instinct has the fewest members in Pokemon Go, and yellow lizards generally don't actively hold and defend territories of their own, instead taking advantage of the fact that Valor lizards have so many females in their harems they can't keep track of them all and mate with unguarded females when the Valors aren't looking. They use small size and coloration similar to that of females to do this. I won't disclose whether Instinct members in Pokemon Go do that, that's confidential information.
Mystic has the most members in Pokemon Go, and both Team Mystic's members and blue lizards gain advantages and territory by working together. Blue lizards are monogamous and focus all their attention on one female. This means that they don't have to compete with each other over females and actively work together, warning each other about intruders and even sacrificing themselves for their comrades. I haven't seen a Team Mystic member do that yet, but I wouldn't put it past them.
So that's great, but what about when the teams interact? But you see, their strategies keep each other in check. This is in reference to lizards, in Pokemon Go, it varies depending on team balance in your area.
Mystic<Valor because Valor lizards possess enough aggression and testosterone to chase off Mystic lizards from their territory, even in large numbers.
Instinct<Mystic because Mystic lizards are too vigilant about their females to let Instinct members sneak in and mate with them.
Valor<Instinct because Valors keep so many females that they can't defend all of them.
And then, we finally have a question. If this happens and the teams are fighting each other, wouldn't one of them eventually win out? Wouldn't evolution favor one team and result in the rest dying out?
The beauty of this is that the teams' strategies counter each other. Each group of lizards keeps one other group in check, and thus everyone gets mates/territory/gyms. And such, by fighting and competing with each other, they maintain balance. In many ways, their competition isn't really competition so much as evolutionary collaboration. Is that true for Pokemon Go? We'll have to see. And by the way-you want to maintain your gyms? Think like a lizard.