As mentioned in the other replies, Google's automatic OCR is limited. OCRmyPDF is designed for PDFs. So if you download a 1000+ page public-domain dictionary off of Archive.org (which is something I do regularly), and you want to re-run the OCR because Internet Archive doesn't tune its OCR very well for multilingual works (if it all), then OCRmyPDF is going to beat Google's automatic OCR every time.
However, I recently paid a programmer to fork OCRmyPDF to give it the option to use Google's OCR engine instead of Tesseract. That fork is here: https://github.com/ualiawan/OCRmyPDF. It's more fiddly than the regular OCRmyPDF, and it requires a Google Cloud Vision account (which charges some fraction of a cent for each page OCRed), but it works well, and in some cases may produce better results than OCRmyPDF, although you must be sure to specify the language of the document.
Very cool - I'm interested in your(?) fork of OCRmyPDF. But can I ask..Why a fork and not a plugin to OCRmyPDF? which supports adding new OCR backends.
However, I recently paid a programmer to fork OCRmyPDF to give it the option to use Google's OCR engine instead of Tesseract. That fork is here: https://github.com/ualiawan/OCRmyPDF. It's more fiddly than the regular OCRmyPDF, and it requires a Google Cloud Vision account (which charges some fraction of a cent for each page OCRed), but it works well, and in some cases may produce better results than OCRmyPDF, although you must be sure to specify the language of the document.