The maneuver you described would not work with a Spitfire as the Spitfire has a greater climb rate. The WEP on Ki84 would not give you any advantage as the Spitfire is more powerful and can maintain WEP for a longer period of time, so if he does not get to you while both WEPs are on, he'll defiantly get you when you loose your WEP and you wont have time to recharge it.
The rate of fire is indeed greater on the Ki-84, but a single 20mm round from a Hispano is more powerful than a Ho-5. I don't know which gun exactly is better, but you can not say that Ho-5 is better just because of the rate of fire.
I don't remember the roll rate on the ki at low speeds so I can't compare it.
Maneuver works just fine and I've used it countless times to ruin many Spitifire driver's day..
Especially after you've made them use up all their WEP...
Got tons of recorded video through-out the years to show that...
Intelligent use of WEP in the Frank will absolutely make it outlast any Spitfire's WEP...(thanks to quick recharge rate)..
Face it... In a Spit, you will probably land or die before WEP ever recharges...
Flap use is important as well.. All these things in combination used properly will make a semi-experienced Ki-84 stick at least have a good time..
Most Spit pilots aren't that great in the first place (hence why they "need" a Spitfire).. Just sayin'...
Ki-84 will also always take WAY more damage than any Spitfire.. 1 20mm hit the wing root of a Spitfire and it's easily over..
I never said it was better.. Hispano is markedly better, but doesn't have the same buzz-saw fire rate as the Ho-5(plus you get 30 more rounds per cannon).. I get in close, fire a micro-burst, and it's over..
Roll rate is better all around(low speeds as well) in the Ki-84..
Plus, I like it just because it's fun and interesting to fly..