The fw190 was very heavy for its size. Three main reasons
1) the terribly bad bmw801 engine. Extremely low power to weight ratio even with c3 fuel
2) The lack of raw materials to produce light weight aviation alloys for structural elements
1) While I don't agree that the BMW 801 was a terribly bad engine, I'd agree that the p/w ratio of it was low when compared with Allied best, especially above 6 km. Germans dropped the ball by not having, at least, the 801E in production.
2) I'd disagree.
3)The unreasonable requirement that a single basic airframe should be able for ALL combat missions: air superiority, heavy bomber destroyer, ground attack (bomb load up to 1800kgr!), long range bomber, low altitude air combat, high altitude air combat. It was very natural that this requirement crippled the dogfighting ability of the mid/late fw190s
IMO, there was no actual requirement to do all of these things.
It transpired that the Fw 190 was found to be well suited for a few additional tasks as the war progressed, just as it was found out that other people's fighter were found to be much more capable than the engineers or the air ministries expected before these fighters entered the production. Eg. see Spitfire, that even became fully navalized, and powered with engines doing more than 100% more HP than in the day one.
High altitude combat was a function of having a suitable engine. It was not Fw 190's fault that Germans didn't have the engine for that task until too late, let alone that RLM didn't pressed hard for, at least, a no-nonsense big V12 to be installed on the 190 for series production.
It was also not the fault of Fw 190 that Germans didn't made airborne cannons that can be a leap ahead vs. the MG 151/20, without these being too big and awkward (MK 103), or with the too low MV (MK 108).
A fighter that is doing well the air-superiority missions is usually also doing well the hi-alt air combat.
1) The most historically realistic: Stick a late Bmw801D engine (2000ps) to a fw190a4 airframe. Reduce the armament to the rwo wing roots mg151/20s. Use the low drag low weight underbelly fuel tank rack . Use the wing of the fw190a6.
I would hope for a normal take off weight of 3700 kgr or less and lower drag because of the removal of the mg17s.
FWIW, when Fw did the similar exercise, they attained the 3660 kg TO weight by removing all weapons but the wing root 151/20s, and also all protection for tanks and pilot bar the armored windscreen. Weight of the protection removed was about 95 kg.
The fully-rated 801D on the 190A4 with over-boost should be able to make 1900+ PS.
2) Less realistic but still possible. A fw190 similar to the fw190 v13 but with the jumo 213 instead of the db603. No fuselage extension like the Dora. Armament 3x mg151/20s.
Use mw50 as early as possible.
I also would hope for 3700kgr ntw, but also 10-11% less drag, far better fuel consumption, better altitude performance. With the eventual introduction of mw50 such an aircraft would be competitive until the end of the war. If c3 could also be used , perhaps germans could get up to 2300ps from the jumo 213a, as the Frenchman did post war
Fuselage extension was probably a very light item, talk 20 kg?
Three 151/20s will weight more than what the 190D9 carried, and the D9 weighted some 4300 kg.
But for germany , the easiest way would be probably to stick an db605asm to a fiat g55 and a c205veltro. And just try to make their production easier. Also the fiat g56 in my eyes looks far better air superiority fighter than the Dora.
Fiat G.55 (and 56) were even bigger than the Fw 190 line, and was the slowest among the series 5 fighters. Being bigger = drag problem = lower speed = not good.
They, together with other Italian fighters, took too much to produce, again not good when one is already badly outnumbered.
The smaller and faster MC.205V with the DB 605ASM or D would've indeed been very fast.