I like the split.
The only score I really track is my K/D. I realize most folks don't care about score, but I like to track this stat for some reason.
And, really, the only K/D that I concern myself with is my LW score.
Before the split I might have hesitated to fly in the other arenas because I'm not as comfortable in alot of those planes and, frankly, I seemed to run into alot more better players in there.
Since the split, I've been using the MW arena as more of a playground. I go in there to fly planes I never fly in the LW arenas- like the P-38. But what I really like are the smaller numbers. Most of the time you can get into a rythm flying against a handful of other folks and have really fun fights. Especially if it's some higher caliber players, there's alot less HO'ing, and a lot more on 200. I've had some epic duels with Oldman22 in there- sort of a running feud.
I for one hope they keep the split as is for now. Mid-war is a great change of pace, at least until you get 5 knuckleheads on all HO'ing in their woobiecanes (looking at you ...th).