Corn in low amounts is not a problem.  The problem can be yellow corn in
high amounts.
 
The fruit content does not necessarily pose any risk factor: again type
and amount, as well as size of the pieces.  Dried carrots and some other
firm dried foods have been known to blockages.
 
Protein content can be higher.  Can't recall fiber content offhand.  Some
fiber is needed to have foods hold together in kibbles, though some new
types of equipment are letting that number be reduced, ditto using starch
molecules which are larger.
 
One ingredient will affect another.  For instance, a highly mineralized
meat source combined with low starch levels can rest in the runs.  It
becomes a balancing act: fitting the pieces together to get them to work
out right.  When a meat source is changed it may be need that the mineral
levels, fiber type and amount, and starch type and amount all need
adjusting.
 
Meat is a very limited food source and is not necessarily better than
meat by products.  It depends on the sources of the by-products and on
the supplementation in the food.  Remember that organ meats are good
sources of many nutrients, esp minerals.  (There are cautions for certain
organs.  For instance, even though Mink Spongiform Encephalopathy (which
ferrets get) is incredibly rare I really would like to see the same food
stuffs removed from ferret food as have been removed from human food for
prion reasons: things like mechanically separated beef, beef central
nervous system tissue, beef small intestine, chicken crops (Chickens
don't get prion disease but the prions remain contagious from eaten
chicken crops of chicken fed infected beef meal for over 2 months.), etc.
[Posted in FML issue 4442]