I've seen you post that before. Is there anything else, something formal, that supports that claim? As we know, combat experiences are complex and don't isolate individual performance aspects well.
Late in the war its easy to see why the P-38J would of been a better aircraft; veteran pilots - even aces like McGuire would disdain the Ki-45. However earlier in the war, not many P-40 and P-39 pilots were aces - you notice far more P-38/Corsair aces because the attrition has already set in for the Japanese War Machine. McGuire himself, thought an "Oscar" was an easy kill and eventually was killed by an instructor with over 3,000 hours (Actually holding on to his drop tanks and turning to tight causing a stall out at low altitude killed him), but he assumed the pilot was a novice - its easy for him to claim the nick was a "terrible" plane; rather the pilots were not the veterans of the early war.
Early accounts showed that the Ki-45 KAIa was a formidable fighter; that could out turn a P-38G - that is all I stated. The P-38G still out climbs and out runs a Nick, one of the benefits the Nick had however was Self sealing tanks vs every other Japanese fighter at the time. Still, the Japanese found out the long range "fighter" was a bad idea as the Germans did with the Bf-110, it simply was not capable as a single seat fighter. Plus the terrible rate of fire of the 20mm proved useless against single seat fighters.
Even if the P-38 out runs it by over 50 mph, doesn't mean the P-38 wins every time; just look at the record of the B-239 against LA-5's. McGuire I believe, probably flew against novice pilots - which makes a difference.