That's correct, you won't get much beyond sort of standard modules for Python. ESXi is a BusyBox, minimal appliance environment by design.
You can, however, do low level XML parsing of your SoapEnvelope, basically, write your own SOAP serializer/deserializer. However, it how much work that is depends on the SOAP interface you're trying to consume.
But, there may be other ways to get your intended result by running automation outside the ESXi host, you should explore that. What is your goal?
Generally, it's recommended that only purpose-build tools be added to the ESXI service console.