The built-in PDF creation of Quartz has often been very low quality and not very controllable. I’ve seen Mac OS create a PDF that’s 100X larger than a well-page PDF with Adobe Acrobat, but I’ve also seen Mac OS create a PDF that’s 1/10 the size, as you see here.
I don’t think that files need to be big or small, but I like to control the parameters and know how a file is created and what compression is used so I’m confident it suits my purposes. If you cannot control the compression parameters with Automator, then I’d take a bit more time and control the downsampling and compression with Adobe Acrobat. If you really want to be detailed, you can also use Adobe Acrobat to ensure your PDFs adhered to the PDF-A standard for digital archival storage.