Very good post SC.
I have a friend, that has a whippet x, that is 12, he has mainly be fed on complete food, along with rabbits ect.
He works like a 2 year old and has, been worked hard all his life!
He has a 14 year old terrier, that still does a bit, again, mainly complete food fed.
None of his dogs, has, ever, had a days bad health, injury's yes, but not bad anything else.
His other dogs average around the 4 to 5 year mark and are very good on the lamp, working most nights!
I, personally, feed both, works well.