Further clarification on 'communicating meaning' with respect to alt text and color contrast needed?

Recently, I've wondered whether further clarification about images
'communicating meaning' is needed, and curious if others have wondered
about this too.

The topic of when something meets the definition of 'decorative' often
surfaces when in discussions with other accessibility specialists, which
naturally also includes whether something needs alt text or not.

'Essential' or 'meaningful' still seems ambiguous. I personally feel it
depends on the context. I've heard folks talk about how illustrations
should have enough color contrast for low-vision users to recognize what it
is. But the images being discussed weren't communicating anything to the
user. They were brand-related illustrations used to help ground the space
and make the page look nice. Another felt that people should have access to
the emotion being exuded by the image. Hearing this, I'm inclined to think
that it would depend on the context, like whether there is value in the
person being informed that a person is smiling.

There's also considering the audible experience and how random descriptions
like 'two hands shaking' sound if it isn't critical to helping the user
understand something. These conversations go in circles.

My concern is the impact of not being able to agree on when something meets
the definition of decorative because of its impact. It affects the people
who are trying to learn from us and those we advocate for.

This topic isn't limited to where I work, but since it came up again, it's
really been on my mind.

Thanks for bearing with my long-windedness and in advance for any 2 cents
that may bubble up.