I don't have time to wade into this now, but I can roughly sketch out a premise:
We have the assumption in the Anglophone world (and the multi-lingual but Anglophone adjacent worlds

) that more power, more guns, more armor was the only way to victory in WW2. I don't think that is necessarily the case though, and a let's say 'revisionist' approach to the history of aircraft like the A6M, Ki-43, MC 202, Yak-1B, Yak 3, La 5FN etc., and then by contrast the P-47, Typhoon, Bf 110 / 210 / 410, Ki-45, yes even the Corsair and P-38 based on their operational histories, tells us that perhaps there was another way- a lighter way.
Operational history tells us that lighter aircraft with fewer guns and a bit less speed or high altitude dominance could also be effective. Whether you needed to be highest and fastest in every scenario depended a lot on the nature of the battlefield and the Theater. Strategic bombing campaigns were not the only way to victory, and where there was a big ground war (or a naval war) going on
below the skies, tactical bombers and attack aircraft were much more important (arguably) than big high flying heavy bombers. Which meant that fighters needed to be able to perform better down low, and needed to be agile enough to win sustained fights around the smaller tactical dive bombers and attack planes.
So there are two tiers to this perhaps. First, we have the known to be successful '
lighter fighters', then we have the more experimental truly '
light fighters' with smaller engines, less guns, maybe non-strategic materials etc., which for the most part, never got real investment or were abandoned by the later war. These would generally be under 3,000 kg gross weight, mostly not used or saw minimal action during the war, mostly using smaller than typical engines (sometimes really achieving a lot in terms of speed with quite small engines ~500 hp etc.) and with small production ranging from just a prototype to maybe 300 or 400 produced. There is obviously some overlap between the two groups, as anything which saw widespread military service goes in the first group.
I probably missed quite a few but I'm out of time ... this gives us something to think about though.
Lighter Fighters might include:
A5M
...