Huh?!!
Absolutely not is it ever better to lie. That's like saying it's OK to perjure yourself to vote for a family member (for convenience or because everybody lies).
Drafting notes for the AA early means the evidence was so strong that it pointed directly to one individual with the motive, means, and questionable alibi to harm SM.
Other investigators were busy completing due diligence, eliminating other potential suspects while Walker continued to build on exactly where the evidence was leading them.
This wasn't an affidavit composed in a vacuum. If evidence surfaced dismissing BM as the primary suspect, pointing in a different location, that's when the AA would have shifted direction.
OP's statement reminds me of a broken heart mother who after a body was recovered from the river within a mile of his vehicle, his school identification, and his clothing, (later positively identified as her son), mom wants to sue investigators for not continuing to look for her son during the 19 days he was in the morgue, waiting for positive identification. (Facts are he was recovered within 10 days of being reported missing, and formal identification required 19 days because he didn't have a regular dentist and visited countless different clinics, and his dental records were fractured at best).
Investigators and the corner told the mother that the recovered body was very likely her son -- especially given no other young men were known to be missing.
So were investigators supposed to lie here too? Tell mother they recovered a female just to give her false hope? And the publicity equal to Gabby Petito?
Investigators don't invent a narrative. Please, they deserve more credit.