I dont think that to many people will agree with you on some of your points.
As for the copy cat thing I do agree with you, that distinction goes to the Russians. However even that Duraluminium did not help the Zero and it still got beat.
I do not agree the Ki-84 was the best aircraft of WW2. Not when compared to the Spit, P-47, and Fw-190. The Ki-84 never reached its full potential do to a lack of construction materials and poor production quality. Performance wise it was not the greatest either compared to the Spit, P-47, and Fw-190 either except for its range.
Crew: one, pilot
Length: 9.93 m (32 ft 7 in)
Wingspan: 11.23 m (36 ft 10 in)
Height: 3.38 m (11 ft 1 in)
Wing area: 21 m² (226 ft²)
Empty: 2,665 kg (5,864 lb)
Loaded: 3,616 kg (7,955 lb)
Maximum takeoff: 3,898 kg (8,576 lb)
Powerplant: 1x Nakajima Ha-45-21 18-cylinder radial, 1,485 kW (1,990 hp)
Performance
Maximum speed: 627 km/h (392 mph)
Range: 2,155 km (1,347 miles)
Service ceiling: 10,500 m (34,450 ft)
Rate of climb: 833 m/min (2,734 ft/min)
Wing loading: 172 kg/m² (35 lb/ft²)
Power/Mass: 0.41 kW/kg (0.25 hp/lb)
Armament
2x 12.7 mm Type 1 machine guns in fuselage
2x 20 mm Ho-5 cannon in wings
2x 250 kg (551 lb) bombs
Production
Total production: 3,514 examples
3,288 by Nakajima
94 by Mansyu
Japan had some great pilots too however I would not call them the best pilots of WW2. I do not see any distinction that can compare them to the aces of Germany, The US, and England.