I researched and made the default skins for all the Spits and Yaks and I can tell you from experience the Spits are much closer to each other 3D shape-wise than the Yaks. The Spits are all variations of the same basic airframe. The fuselage aft of the firewall, gear, wing and tail are essentially the same, but with different engines, wingtips, props, rudders and guns etc. They all use the same cockpit art.
The Yaks are based on two different airframe series. The Yak-1 was a small lightweight fighter and has more in common with the later Yak-3 than the 7 or 9 series but still less than any two Spits. The Yak-7 was a larger airframe developed from a two-seat trainer and designed to carry a heavier armament. The Yak-9 series was developed from the 7 but the Yak-9T we have has the cut down cockpit moved aft on the fuselage and a different wing shape while the Yak-9U has the wing mounted further forward on the fuselage to balance the heavier longer engine.