This subject splits into genuinely different problems
BetterPicTreating professional portraiture as one topic is why so much advice contradicts itself. There are at least four distinct problems underneath.
Choosing a tool
Where the criterion is not sample quality — every product does well on an easy face — but whether the output still looks like the specific person, and whether it can be reproduced later.
Understanding how the images are made
More useful than it sounds. Knowing that the system learns what is constant about a face explains why fifteen photographs from one afternoon produce a portrait of your shirt.
Industry conventions
Which genuinely contradict each other. Medicine wants warmth, law wants restraint, and no single headshot satisfies both.
The technical baseline
Contrast between hair and background, crop, light direction. Universal, measurable, and unaffected by any of the above.
Why the split matters
Because most disagreements in this subject are two people answering different questions. Naming which problem you are solving resolves more of them than any amount of extra advice.