The claim a portrait can actually support

The marketing overstates it and the backlash understates it. The accurate version is narrow and more useful than either.

What it does not do

Make anyone appear more qualified. Nobody has read a CV and revised their assessment of someone's abilities because of the lighting.

What it does

Prevent one specific failure: someone briefly willing to look at you scrolls past instead.

Why that is worth anything

Because most weak headshots are not unflattering, they are unreadable. Cropped too wide, eyes in shadow, a head with no clear edge. The viewer is not judging you badly — they are not seeing you, and there is nothing to react to.

Where the value accumulates

Not in any single view. You appear in hundreds of lists over years, and a legible portrait in each is a small repeated advantage.

Repetition rather than impact. A duller mechanism than the one usually described, and a considerably more reliable one.