Does the webpage you are embedding this image on resize with the browser window/device screen size? If so (which it should) does this image appear at all breakpoints, including small screen sizes? The text embedded on that image may look great and be an easily readable 42px font when that image is 1400px wide, but when the same image is displayed on a mobile phone and the image is resized to fit the 320px screen the embedded text will now be a 9px tall non-sharp mess.
As you stated, text that is embedded in images is not able to be read by people who are visually impaired. It is also not visible to search engine crawlers who are trying to index the content of the page. While this can be remedied by including the quote in an alternate text tag, it may be confusing to people using screen readers to hear the quote twice. The alt text can be left blank to counter that, but now visually impaired users are not receiving the same content as visually capable users, which is the whole point of accessibility.
You mention that quote in the image is already shown on the page. Screen real estate is important and so is minimizing cognitive load. Why waste both by showing users the same text that they have already read on the same page?