Progressive Politics

This is among one of many techniques presented at the WCAG site you linked. You putting text in a top level comment would seem to me to satisfy this, at least in intent.

Not in the slightest: the guideline falls under Principle 1 – Perceivable

Information and user interface components must be presentable to users in ways they can perceive.

as Guideline 1.1 – Text Alternatives

Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.

The sight-impaired user is unable to perceive the text content hidden in the image at the post listing level that the sighted user can perceive. Your suggested text alternative is simply not there to display at the post listing level. Your suggested execution of the technique fails its test

1. Remove, hide, or mask the non-text content
2. Display the long description
3. Check that the long description conveys the same information conveyed by the non-text content.

since we can't display a description absent from the page. Your nonsolution misapplies the technique & is not a credible text alternative.

Imagine opening every post to seek among an unsorted mass of comments a comment we can't seriously expect to exist providing a text alternative not written by the author & of questionable integrity: the user has no incentive to take that additional effort for a post that already violates web accessibility. They may not even be aware a post needs a text alternative. That is not equivalent to the experience of a user who can read the image.

The best solution is not to use any web accessibility technique: actual text doesn't need it. Sharing it as an image was gratuitous & unnecessary. The post could have been proper text with the same bolding & line breaks.

to offer and make accomodations to the best extent possible

which your nonsolution here definitely is not: the post remains inaccessible. That is not due to a limitation of possibility: it's due to a failure of will or execution. As originally stated, posting proper text or setting alt text is possible.

A separate comment only gives the commenter an unfounded sense of accomplishment, when they're only enabling the posters to continue violating web accessibility without any pressure to correct themselves. Structurally prolonging dysfunction that way is the opposite of helpful.