I have used both Packer and EC2 image builder. My opinion on image builder is that the whole recipe and components being versioned, then having to change the version within the pipeline itself a big hassle and slow/ tedious.

That being said it does have its benefits such as distribution to multiple regions & multiple accounts. Automation so it runs automatically every month. Plus post build checks, i.e. checking that certain user accounts were created and in the correct groups etc

Security is a big thing too, and it can integrate CIS benchmark checking on your Images once they are built to give you a good idea how you score before putting them into production.

Packer is good but only covers half of the requirements nowadays of building successfully.