That is a possibility, but I can’t say for certain without parsing the log file, grouping the files and adding the different groups together. Here’s two example lines from the log. The mentioned components have no relevance in my project:
Kicad includes the most files from the project-directory (inclusive all sib-fiolders) into the project-archive. The archive-algorithm doesn’t checks if a file is used in the project (or only forgetten from an older project).
The check if a file is zipped into the archive uses the file-extension, so the following files all get into the archive:
all step/stp files
pdf-files
all gerber-output-files
all kicad-related files (all project, board, schematic, library-files, independent if they belong to the project or not)
So to reduce the archive-size you should delete all files which don’t belong directly to the project from the project-subfolder.
You could also look into directly into the archive and search for the files which need the most space.