<S>
I remember the discussion about 150 grade fuel in 2016. It was discussed for at least a week with input from several people. Two of the most decisive arguments were about gameplay balance and most importantly about historical accuracy.
Gameplay balanceThe Spit IXe and especially Spit XIV are already among the absolute top notch fighters of the game. This has evened out a bit now with new flightmodels being released. While most late war planes can usually excel in one or two areas like top speed, turn rate, climb or roll rate etc, the Spit XIV is very competitive in nearly every aspect. In the last S3 series it whooped the butt of the Axis Bf 109's and Fw 190's with a kill ratio of 101/20 (5.05 positive ratio). If the Spits were given 150 grade fuel boosts on top of their already great performance, then it would probably make Spitfire lovers very happy. It would however screw the balance for everyone else and we could soon see only Spitfires fighting Spitfires in the late RPS. The gameplay balance aspect is the same reason as to why the Me262 isn't enabled except for the odd day or two.
Historical accuracyAs I remember the historical aspect was however the most deciding factor for not giving the Spit IXe and XIV the 150 grade fuel boosts. The P-51D new flightmodel was given a 150 grade fuel 72" Hg WEP first after a thorough discussion, were plenty of evidence was put forth that this fuel was actually of widespread use in fighter vs fighter missions in ww2 for the Mustang. This was as such representative for the P-51D's performance when fighting enemy airplanes. The Spitfires however almost exclusively used 150 grade fuel for V1 hunting missions. This fuel was very expensive and only used on rare occasions for air superiority missions vs Luftwaffe fighters. The absolute majority of Spitfires that the Luftwaffe pilots had to fight did not use 150 grade fuel, as it was reserved for the squadrons protecting London from Hitlers bombardment. In the Legacy Arena you are fighting other players, not hunting V1 rockets. As such for a themed S3 series the 150 grade fuel boosts could be correct, but in the normal arenas it would not be representative for the Spitfire's actual performance in ww2 dogfights.
If clear evidence can be brought forth though that 150 grade fuel was indeed the norm for Spitfires in air superiority missions, then this could of course be implemented.
Cheers!
/Robert