No rodents? Are you twenty years behind in your varanid literature? If proper husbandry conditions are met (high humidity, basking temps of 120-140F, lots of space and hides) then there is nothing wrong with a predominantly rodent diet. The problem with rodent diets is when the animals are kept in tiny enclosures that are too cool. Proper digestion is not possible.
A rodent (mice or rat) is a complete diet. Millions of snakes can't be wrong, can they? What's the difference between an active monitor and a lazy snake? From what you're saying every snake in captivity is doomed to obesity and a short lifespan.
I've been keeping varanids since 1990, and they have all been fed a predominantly rodent based diet. My first niloticus lived to be 16.
Chris