Answer
If multiple metabolic pathways produce the same or similar products, it points to multiple ways, with different steps, to produce those products. Since not all such pathways have the same length, then not all intermediate steps would necessarily be required to produce the product and might be added later, further along in evolution.
Work Step by Step
The "too complex" argument generally relies on the estimation of probabilities of various events, a highly uncertain work at best. The works of Stanley Jaki often deal with questions like these-- they may be of interest to the student.
