It depends on what you mean by "image/media-heavy". If you have a website that is basically made of image galleries, you can still make it accessible for blind

It depends on what you mean by "image/media-heavy". If you have a website that is basically made of image galleries, you can still make it accessible for blind people by giving descriptions of each picture. The problem is that describing a picture is hard: if you have a picture of a generic tree, you can give it the caption "A tree", but what if you want to give details of your hypothetical tree? To continue the tree metaphor, you shouldn't miss the forest for the trees: a blind visitor may want to know each detail in the tree, but most blind visitors just want to know that the picture has a generic tree so they can move on to find the information they actually need. With videos, subtitles/captions are useful for deaf users, and useful for blind people when a video has no narration, just a soundtrack. I say the reason screen readers are given a higher importance than unusual or outdated browsers is a matter of being able to choose. When you use an old browser, you can choose to upgrade. When you have a disability, you can't choose to not have that disability: you're stuck with screen readers until a better way to browse the web with your physical constraints is found.