why packer doesn’t allow (like a make process) to reuse stages artifacts to avoid running always all stages: build, provisioning, post-processing.
image build from iso + kickstart is an heavy stage. Consolidated base image from various builders (ovf. from vmware-iso/virtualbox or other image data) can be reused in subsequent stages (provisioning, post-processing). The same for provisioning and post-processing, so one can consolidate/change each stage focusing on the next or apply change/debug intermediate stage without long running processes.
A make like approach would be very productive and efficient. Probably using state files to record stages info.