Is the current API testable? So many times I've taken ownership of code that requires an active connection to a database to even be up and running. Changing the code so it's testable usually changes the code so much it is very hard to have confidence it works the same way as the original implementation.
My old company lived and died by its instrumentation of DAU (daily active users). We would try to refactor the code to an IoC pattern with DI but invariably we'd get blamed for a downturn in the numbers - but never lauded if the reverse was true. It was a losing game - we finally had to get management to commit to the modernization (never, ever say "rewrite") and power through the days of low DAU.
My old company lived and died by its instrumentation of DAU (daily active users). We would try to refactor the code to an IoC pattern with DI but invariably we'd get blamed for a downturn in the numbers - but never lauded if the reverse was true. It was a losing game - we finally had to get management to commit to the modernization (never, ever say "rewrite") and power through the days of low DAU.