Cleanups to implementation of create()

[dstansby]

This cleans up the implementation of create() a bit by:

• Fixing the typing of filters
• Removing duplicate parsing of data type and compressor (the parsing is already done further down the call stack)
• Moving the parsing of filters to be in the same place (further down the call stack) as parsing of compressor

[d-v-b]

thank you for this cleanup work 🙏