Your speculation has been extensively explored, and isn't actually better than the theory advanced in the article:

http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=D...

Reading over a few of the abstracts, the consensus appears to be that depression can be caused by defects in circadian rhythm, but that the relationship isn't necessary, and may not be sufficient. If I were you, I'd ease off on using "amateurish speculation" as an epithet in this situation.