What's the reason you've chosen MySQL over the bind backend when you are using the API anyways? I have to make a similar decision soon and I am not really sure yet, any insight would be appreciated.
Full access (read and write) to the PowerDNS HTTP API requires one of their generic SQL backends (via https://docs.powerdns.com/md/httpapi/README/), such as MySQL. The bind backend only supports reading from the API, changes to zones would need to be done on the file system and/or using pdns_control. Beyond that having all our records queryable via SQL has been nice for debugging and researching our own DNS records, types and etc. Lastly, backends like the MySQL one allow for things like auto generating serials and adding comments to the DNS data.