Yak-9U is actually making up to 1750hp (in a narrow altitude range), though. Not up high where it gets its top speed sure, but the same goes for the D.3803. All are very cleanly designed aircraft.
That being said, the 109 G2 is doing 680kph on ~1500hp (pretty high up by 6km), so this might not be as outlandish as it looked at first. Given their similarities they should be quite close on performance…
YS-3 also has another disadvantage in that it uses a single stage, single speed supercharger. Peaked at 1600hp at 4700m. The Saurers are likely just license built 12Zs.
Yak-9U is actually making up to 1750hp (in a narrow altitude range), though.
The VK-107A engine that lacked water injection was quoted several times at 1,650 hp - this is the engine the war-time Yak-9U used. The 1,750 hp figure comes from the later version when they ironed out all the kinks, added water injection and boosted the RPM - this is the engine the Yak-3 VK-107 and post-war Yak-9U used.
The Saurers are likely just license built 12Zs.
They most definitely are not. The original Saurer YS engine was a licensed version of the 12Y engine, the 12Z didn’t exist when Saurer got the license.
The YS-1 was almost exactly the same as the 12Y, the YS-2 was a major overhaul with a much heavier crankshaft (47 kg to 80 kg), beefed up internals increasing weight to 684 kg compared to the 12Y’s 429 kg, and 4 valves per cylinder opposed to the 12Y’s 2 valves per cylinder. The YS-3 was even heavier still - up to 705 kg. All of this was done to cope with the increased power of the engines.
The concept is fundamentally similar to the 12Z, but a licensed version they are not.