This is a well documented consequence of the ABBYY OCR engine that DEVONthink Pro Office licenses.
Threads:
There is very little that can be done to reduce file size without a commensurate decrease in image quality.
Adobe ClearText (since rebranded I believe) is one of the only (and I’d say, the best) ways to accurately OCR a file and (usually) decrease the file size. However, the catch is you need an Adobe Acrobat subscription which runs pretty steep.
DEVONthink’s OCR is ver accurate, but does inflate the size SUBSTANTIALLY unless you really scale back the quality. It’s an unfortunate tradeoff. I am not normally able to sacrifice quality since many of the scanned things I have are long form reading, and I can’t tolerate looking at pixelated text for hours. I use the OCR in DEVONthink very rarely for this reason, though periodically I will use it for smaller things that I forget to OCR when I scan them.
My hope is that ABBYY eventually develops a more space-efficient engine that DEVONthink can license, or DEVONthink find’s a different engine to license.