Why fleet fixes had to begin before the war

Could changes to individual Axis fleets alter the outcome despite their industrial weakness?

Only at the margins; their infrastructure and industrial position made the war strategically unwinnable without changing the wider conflict.

Some naval choices were correctable, while national-scale weaknesses such as codes, infrastructure, and industrial capacity lay beyond any fleet's control. A navy could improve its own cryptographic practice yet remain exposed when other services kept using a compromised system, as German confidence in its codes demonstrated. Meaningful fixes generally had to begin between 1934 and 1938; by wartime, the underlying balance made an Axis victory extraordinarily unlikely. A better fleet was still very different from a state capable of winning the wider war.