Perhaps, but .7z archive format raises some issues described here by the original Duplicati developer.
What would be more reasonable would be to stick with .zip archive format, and change compression:
--zip-compression-method (Enumeration): Sets the Zip compression method
This option can be used to set an alternative compressor method, such as
LZMA. Note that using another value than Deflate will cause the
zip-compression-level option to be ignored.
* values: None, Deflate, BZip2, LZMA, PPMd
* default value: Deflate
I would note that LZMA2 format uses a mixture of LZMA compression and no compression. Duplicati’s handling of incompressible files is to recognize those files by their file extensions. List is changeable in compression-extension-file. For better compression, you can also raise blocksize from default 100 KB.
Each block is stored as a (maybe) compressed file in the .zip file. Compressors might like larger files.
The options are limited. Over time, I would guess that compacting would recompress some dblock files.