I understand how someone could arrive at the conclusion you describe, especially, if this conclusion was contemplated without considering more complex and elaborate scenarios.
The problem with your theory of the crime is it’s too simple, I’m familiar with Occam’s razor and agree that in most cases it would apply but I don’t believe this case is a candidate for such consideration. I say this because the event you describe would not have been a small error made by the culprit but a glaring road sign leading LE directly to the person and directing their attention away from any other potential suspects.
I realize that most criminals make stupid mistakes, and this is the caveat that gives me pause with this case. There were no mistakes made other than this one glaring huge mistake, it doesn’t make sense that the murderer could be so thorough and competent in every other aspect of the crime, yet do something that is obviously going to implicate them.
IMO, this is a classic example of a frame up, considering the origin of the check printing evidence was a computer that DK potentially had access to only adds more validity to this theory. DK also would have known that Merritt would have had no problem accepting a check from JM to cash, we also have no idea who really made the call to the QB’s help desk.