DEVONthink Pro Office does have the ability to OCR using built in ABBYY OCR software. This can only be done on the Mac.
DEVONthink To Go cannot perform OCR.
As you’ve discovered there are other options, such as that built into Scanner Pro/Scanbot, or dedicated OCR software like that offered by ABBYY on macOS and iOS. My experience differs considerably from yours so I figured I’d outline it here just in case it offers some insight. Certainly it is in no way an attempt to debate or deny your experience!
Personally, I’ve had largely positive experiences with OCR in Scanner Pro. In general the accuracy is more than sufficient. I just checked a few invoices I scanned and OCRd with Scanner Pro and the entirety of the text is selectable, and checking about 15-20 words indicates each one is correctly identified. In my testing I selected mostly the types of words I would want for searching: Dates, business names, etc, and those were all correct.
MANY of my scans are 1-3 pages, and I find that OCR only takes 10-30 seconds depending on the amount of text on the page, normally this task is completed during the time it takes me to rename the file in Scanner Pro.
The PDFs generated by Scanner Pro, including OCR, is of nice, crisp visual quality and high resolution, and the file size is modest. This is in contrast to the experience I have had with DTPO’s built in ABBYY OCR which tends to significantly inflate file size unless you significantly degrade the quality.
But, of course, this is just an anecdote. I can’t account for why your experience is so different from mine, but of course the accuracy of OCR is highly contingent on the quality and clarity of the scan. My scans with an iPhone 8+ and previously an iPhone 6 generally produced images of sufficient quality for OCR to be adequately performed yielding the results I outlined above.
Scanbot may handle OCR in a different way that produces better results than Scanner Pro under the conditions you are scanning, which may account for why it worked marginally better for you.
There are so many variables that could contribute to your experience, thankfully there are a lot of tools! I hope you are able to find a tool that works sufficiently well for you!