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While running missions to get mods i noticed i can get Split vs Argon, but not the other way around, do they argon just not care because the Xenon usually just stomp Zya?

There's no ARG vs SPL missions at all. Like you said only ARG vs XEN.
Argon fights alone against Split (they are so powerful that don't need help)

And we need Boron vs. Split, and Split vs. Boron, and everybody against the Xenon, and so on. The mission selector would likely need a makeover to deal with all the possibilities!

Because lore wise, the Argon in their sectors near Zyarth's Dominion should not be in a position to make offensives, as shown by the encylopedia entries of Eleventh Hour and Guiding Star. It's why they only have a Wharf to start with.

In the game however, they just siphon destroyers by moving them from their home sectors through Teladi space to reinforce Eleventh Hour, so their influence is not as weak as it's supposed to be and end up building up a massive amount of forces.

Xenon stomp ZYA, then ARG goes through Heretic's End and flushes Xenon from former ZYA sectors. End result is the same, top of the map colored blue.