Completely agree. I tried scaling down the PDFs but Ghostscript on the Raspberry Pi is far slower than just scaling the 1200px wide PNG to 800px. I still got very readable barcodes, and a 100% delivery rate on my first batch of orders, even with that downsampling.

I could be wrong, but I don't think pixel perfect barcodes are necessary with modern scanners. The only thing going for ZPL is the ability to store the label data as simple ASCII text.