Hi,
You do not have to remove the usage of DownloadableResource. The DownloadableResource is specifically designed to download and optionally extract files from a remote host. This involves processing and storing the binary data that is received.
The HttpRequest only covers an individual network request and handling the data is up to you. It would be cumbersome to implement your own file download and process binary data in QML/JS. For this use-case the DownloadableResource is here.
So you can use HttpRequest only for the POST request if that is what you need. It does not matter where the data you post comes from and if it was previously downloaded using DownloadableResource. In either case, you would create a POST request with the HttpRequest item.
Best,
Günther