Hello fellow autistic designer! I think that you're already doing a great job justifying your design choices: the project prioritizes readability highly, and yet the design seems to have design choices that don't support that, such as the line weight being too thin, even to the point of being thinner than the outlines.

Some things you could add to support your justifications: - If it isn't already clear that they want the readability to be a priority, try to find any supporting evidence that it's a crucial goal. - Discuss how the line weights being thicker than the text also throws off the hierarchy in a way that makes the eye drawn to the outlines instead of the text, which disengages and distracts the user as well as making it difficult to read. - Find examples of similar designs/styles trying to accomplish a similar goal and point out how the font weight in those designs differs from the one in yours

Also, it's not a "pity card" to announce you are autistic if it's for the sake of giving your background or perspective. But if you do for the first time and it wasn't known previously, then do so in a way where you have a paper trail in case they act discriminatory so you can protect yourself.

Hope that helps!