The weight question was moreso about if the engines would really need to develop as much power as their contemporaries as long as both the engine and the aircraft themselves are light within reason (AKA not one of those light fighters). Something more or less like the Yak-3 as an example, since that was quite rapid despite its low power.
Would the 12Z and the 14R need to push past the 1,300~1,400 hp and 1,600~1,700 hp marks respectively given the light weight of both the engines themselves and the aircraft they were intended for? Cutting down on the required power might also allow them to focus on reliability.
A lot depends on what you want the planes to actually do.
The Japanese and Russian aircraft were not as well protected as British/German/US fighters. Not all self-sealing tanks offered equal protection and be careful of the phrase "protected tanks" as that was 'achieved' in several ways. Sometimes it was duralumin sheeting (light-thin armor), heavy rubber bags, sheet metal tanks that purged every so often with exhaust gas to reduce fire risk (did nothing for leaks).
The Yak-3 it trotted out in the light weight fighter crowd all the time. How long did it take to show UP? What could it do when it got there (it was fast). What couldn't it do? It did well against the 109s/190s over the eastern front in the 2nf half of 1944, at low altitudes. It was never fitted with bombs or rockets. Armament depended on light guns and somewhat limited ammo capacity (20mm was hard hitting while the ammo lasted, 9 sec) It didn't fly quite as well as the bigger Yaks and they all had issues, like weak/unreliable landing gear but HEY! the landing gear was light! They also had primitive instrumentation and not very good radios......................but the instrument panel and radio were light! Seeing a pattern here?
Light, ill equipped fighters can do a good job in certain roles
IF you have other aircraft to perform the other roles. Higher altitude combat, longer range combat, bomber interception, ground support.
The Ki-44 had light armament most of the time. It could carry a pair of 100kg bombs (or 130 liter drop tanks).
Now, do the French need to push past the 1300-1400hp mark to deal with the
heavy 109s?
Let's remember that the Germans had gone from about 1100hp in the middle of 1940 to about 1400hp (if things worked right) in the fall of 1942. Depending on 1300-1400hp engines in 1943 and later and light weight construction depends a bit too much on knowing what happened.
The French are forced into light weight fighters because of their engine as it is. They were trapped in mid to late 30s and there is no way out without some unknown design popping up or building Allison's/Merlin's in France which was not going to happen unless much of France stayed Free in 1940. It wasn't going to happen under a Vichy or Vichy like arrangement.
As far as engines go, a lot things happen behind the scenes. Allison got very lucky several times and not so lucky a few times.
Allison found a new way of casting crankcases/cylinder blocks (developed by a husband-wife team of artist/sculptors, not by Allison) that allowed for stronger parts and more precision (less machining after casting) and might have even saved a few pounds. Allison didn't invent nitriding but when they nitrided their crankshafts they gained a huge amount in fatigue resistance. The two together allowed Allison engines to stand up to a large amount of abuse (war emergency power). On the other hand, in late 1941 Allison was trying to make engines with higher supercharger gears to add several thousand feet of altitude to the engines. But the way the Allison is designed the supercharger gears can only be so wide to fit in the housing which is cast into the crankcase (then covered with the auxiliary back plate) and the increase power needed to drive the supercharger faster stripped the gears in a short period of time. It took almost a year to get the block castings and auxiliary back plate cover sorted out to accept the wider gears.
The Allison was strong enough to hand 1400-1500hp at WEP running on 100/130 fuel which greatly reduced the need to fit a two speed supercharger (using the original supercharger) however that was not the fuel the engine was designed to run on. Allison then dropped the ball on the two mechanical stage engines.
