This is a great question. We'd love it if the synthetics world was more standardized, but unfortunately, since the tools are so complex that's not really been done in a substantial way for most use cases. Synthetics tools tend not to cross-compatibility or import functionality due to their complex nature. Elastic Synthetics is no exception.
There are some sort of halfway attempts some tools use solve this, like Proxy2JMX, which states on its website "only requests will be converted, no assertions or other logic". We've avoided this approach because it still requires manual intervention to ensure that you're truly only testing a plain navigation use case with no logic. I imagine that sort of tool is more applicable to load testing where you are more likely to have simpler linear journeys.