Keep in mind that these records were intended only for their purpose e g tax collection, church records and censuses and not particularly for future generation genealogists. Many records have been lost through fire, water penetration, pest infestations and human neglect such as disposing of records. Anyone researching getting beyond 1837 and relying just on parish records is doing remarkably well especially if there is a single forename where guesswork rather than accuracy takes over. I have come across many family trees where imagination and guesswork proves to have no real evidence to substantiate the research.
I think that you should be very grateful that any research goes back beyond 1700 and apart from parish records existing since 1538, Visitations [records of nobility claiming a title] and Wills [sadly Devon lost many in WWII] there is no magic source to lighten the search by a family historian. I always use the adage it is better to have a short accurate tree rather than a long spindly tree full of guesses and inaccuracies.