I see you about the lack of kills. The Xwing is particularly awkward in that regard, because if you include Integrated Astro, it starts hypering out at literally half HP. the Ywing and Bwing go at 3/8 and the Awing hypers at 1/4 hp.
I am OK with small changes to the Xp system like adding or changing entries, but your suggested tiered communal XP is a bit harder to swallow. Making both Kill and Rebel kill communal feels better to me- hunting down an Ace Xwing is then worth 4 XP to the killer and 3 XP to everyone else in the (potentially 12 strong, if their using the half-ship Tie Fighters) Tie Swarm.
Perhaps if the Xwing hypers at 1 HP+integrated astro, instead of 2, that might make them more killable, too. It would put them in the same range as the other rebel ships.