Nobody would want strat ticks for fighting in strat battles over getting 500,000 XP (well not most people, maybe some of the people who only play strategus battles and don't play in the public servers).
I don't see any down side to getting strat ticks for fighting in strat battles, it's a no brainer that you should be getting strat ticks for actually playing the game.
Independents can get into strat battles if they sign up, are a high enough level, and are there for roll call. It helps if you're good and people recognize your name. If you're really jonesing for a strat battle, then join a clan that fights in them, or join a friendly faction to those fighting. There's always extra slots for non-affiliated players or factions in every strat battle. Every single one.