V-2 engines were dealing with much higher temperatures and used a lot more strategic heat resistance metals like Nickel.
Well I'll take your word on that.
As to the fuel types of the rockets, you have to walk before you can crawl, so the work done earlier enabled later, more advanced designs.
On that principle, did the development of jet engines begin in 1910 with Coanda?
Also you cannot simply divorce the overall ballistic missile systems package from the engine, as the engine is pointless without a means to actually deliver it.
We definitely can divorce the rocket engine from the V2s, which was a means to deliver an explosive, not an engine. We can do that because rocket engines went into other stuff than the V2, such as the Me 163, which had its own guidance device.