Raptor 2 has melting issues that prevent many of reuses. It not just gone melt during operation. They have tested Raptor 2 full flight cycles many times.
What they are doing is trying to figure out how much cooling they need to make many reuses possible but still have the highest possible performance.
Soviets were desperate by then, no money, no time, and political pressure.
> How did Musk solve this problem?
Raptor 2 apparently has melting issues, you can only imagine what will happen when you have whole array of them firing.