Modern books - and for that matter genealogical websites - are inconsistent too, and can be just as inaccurate as older ones. Even Douglas Richardson, who is often regarded as generally trustworthy, acknowledges in his prefatory material that some of the key sources he has drawn on can be inaccurate and are incomplete.
The reliable source lists will always be very incomplete, and that is, I think, entirely recognised. It would be arrant nonsense if a tweak in wording of guidance for project-related pre-1700 profiles stopped what is self-evidently good and sensible practice. When I use books, as I often do, I am frequently thinking in terms of “does this book give reliable information for this particular fact or this particular relationship or the existence of this particular person?” That must surely be the right approach. If a book of any age gives a transcription, quotation or translation from, say, a will, deed, official record, tombstone inscription etc etc etc, then, unless there is some strong reason to do otherwise, I will generally trust that transcription, quotation or translation even if there are other things in the book I do not trust. As Jillaine has said, what matters is the quality of the sourcing used by a book or website - and often sourcing is far better for some things than for others.