The 31-year-old only managed nine goals in almost 50 appearances but Kenyon insists Shevchenko should not be labelled as a failure.
"I get fed up because it's not right," he said.
"I'm not giving a lesson on accountancy, but you do write money off over the term of a contract.
"What we pay is in an investment. During that period you have a player who is doing a job and in this industry you buy and sell players."