This isn't like lossless compression. Both techniques involve throwing lots of information away, with the justification that doing so does not significantly affect the end result.
The extent to which using both the techniques together will help will depend on how much overlap there is between the information each ends up discarding.
Modern LLMs are still quite inefficient in their representation of information. We're at like the DEFLATE era and we've still yet to invent zstd where there's only marginal incremental gains; so right now there's a lot of waste to prune away.
The extent to which using both the techniques together will help will depend on how much overlap there is between the information each ends up discarding.