Hello to you Brushbroomstick,
We too are descendants of the Joseph Fletcher who married Ann Powis. Thereafter and up to date the records are clear and the family line directly traceable through the BMDs up to today. As you say its the generations before Joseph and Ann that are problematic. I suspect that Thomas and George are brothers or cousins and equally possibly the father of Joseph. But they are still 'family' and if you are working back in time then they are both from the same immediate family. I have been chasing the same line for sometime now and did hand search (online) each and every page of the Little Wenlock parish records for that time frame. In fact there are not many Fletchers there and the settlement is not that big. The parish register is quite well preserved as I am sure you know already.The family are Ropiers and this is directly mentioned under Little Wenlocks entry in British History online. The family I have are not originally from Little Wenlock. They are displaced during the English Civil War and are in Sutton Coldfield according to my research. Originally I have the family coming from Lapworth, displaced during the Civil War John Fletcher (being the father of George and Thomas Fletcher). Because the Civil War period is so difficult I pursued double tactics. Firstly I tackled the matter by looking at lineage (george son of........ etc and dates). Then I checked my findings by casting the net really wide and looking at all Fletchers for each time frame gradually reducing the the likely fits by dates, location so on and so forth. It has taken over five years but in the end I have the 'Best Fit' for the Civil War years and earlier. It might be all I can get but I can't help noticing that the settlement populations are really quite small and with only a handful of Fletchers which probably means that they are siblings or cousins (using the Consanguinity table).
I sincerely hope that the above ramblings are of help to you and wish you well with your research.