DEVONtechnologies focusses on database tools that facilitate use of information provided by a variety of document types that may be captured within a database. Development focus is not on development of proprietary document types, but on accommodation to management of document display in OS X code (including Quick Look) or in third-party applications. DEVONthink doesn’t write text editors.
Rich text isn’t dead yet. It still has advantages in file size for easy accommodation of font formatting, images, links, tables and lists. Most of my notes can be copy/pasted in one pass to Pages without loss of features.
The problem the OP stated is that text documents printed within DEVONthink do not preserve the font size specified for the document, but will print out text with smaller than specified font size, that grows smaller the wider the text window happens to be. That’s the result of using the plain and rich text code in OS X.
There are three possible solutions (other than recreating text code by DEVONtechnologies): 1) A messy kludge, reduce the width of the window in which the document is displayed, in order to make the print size larger (but the font size isn’t sacrosanct). 2) Reformat the text to force page orientation and margins, like the Wrap to Page mode of TextEdit e.g., use the Rewrap content to fit page option in the Print panel (I would prefer this to permanently changing formatting, as it will continue to allow text flow to accommodate window width for onscreen viewing). 3) Transfer the text content to another text editor that includes page wrap and other features such as header/footer, etc. for printing.
I prefer option 3). That lets me control header/footer (unlike the option in the Print panel to add header/footer) and may use footnotes or endnotes. I almost never print notes to paper, but frequently do convert them to PDF for distribution to others. My note specifies font and font size and those choices will be carried over in the transfer to a more full-featured text editor.
For simple tasks I open the text document externally in Bean, add the title as a header and page numbering, e.g., 1 of n, and print to paper or as PDF.
For more complex layout I’ll usually copy/paste the document into Pages, which carries over in one pass images as well as text (MS Word won’t do that). From Pages, after final polish the document can be printed to paper, to PDF or exported as MS Word.
I should have mentioned the Print panel option to wrap text to page. I don’t use that myself, as I want more control, especially of header/footer.
There was a time when TextEdit exhibited the same phenomenon for printing in Wrap to Window as does DEVONthink – increasingly smaller font size as window width increases.