If the tips stalled first the airplane would be very wicked at the stall. Designers always want the root to stall first. There is more than wing planform that effects how the wing stalls. Washout (the twist in the wing putting the tip at a lower angle of incidence than the root) prevents/delays wingtip stall.
You speak in great generalities and in this case 'wicked' would be correct if the pilot doesnt realize what is happening. All WWII fighters can be wicked if handled poorly. Washout is designed into aircraft to alleviate tip stalls in elliptical wings and in wings that have a tapered leading edge like the Me262.
The reason the P-51 experiences buffeting of the tail during stall is not because of the root stalling first (which doesnt happen anyway) but because the downwash of the wing causes an increase in induced drag. If you were to picture the induced drag of nearly every plane in WWII you could see it as slight turbulent flow above the wing behind about the 60% point on the chord (actual percentage varies by airfoil obviously). In the case of the P-51 you would not be incorrect by picturing that as occuring behind the wing altogether.
This is why when the RAE went looking for a combat aircraft to fight the Luftwaffe above 30k they found all allied aircraft wanting except the P-51. While the luftwaffe was fielding aircraft that could fight at mach 0.75 the P-38 was only capable of fighting up to mach 0.68 and the P-47 at mach 0.71 while the Spitfire itself was too fragile to handle combat at high speeds. But the Mustang saved the day because it could fight at mach 0.78 and because of its design (laminar flow and very low induced drag) it could manoeuvre at high speeds at high altitude very successfully.