Thanks to all who replied- this was meant to go under the unperk Spit14 thread but couldn't delete it
As has been stated it's not exactly great down low which is where the majority of fighting now happens.
Still, no-one has given a definative answer as to why it is perked, and then proven that there isn't a "free" plane that doesn't fall under the same reason.
If you use -
1) Numbers made, there are free ones under that category.
2) To prevent overusage, guess the D9, Pony, and Lala fall under this.
3) Performance, could lump a whole load of free stuff into this reason.
Don't think if it was unperked you'd see an MA full of Spit 14's, the Spit 5 now sees more usage than the Spit 9.