Force media library to show only large images, not full size

I have an issue where I don’t want the full (original) size images to be what is shown on the media library screen or “Add Image to Gallery” modal screen; I’d like to show the “large” version of the image instead.

Reason being, I’m hiding the original size images via .htaccess and it’s loading a broken image element on these screens. If I don’t hide it via .htaccess, the images are so large they take forever to load (even as thumbnails since it’s using CSS to scale them down, not using the thumbnail file to show them, which is what I kind of want).

Before it’s mentioned: the solution cannot be resize the images before you upload them — that’s not a possibility in this case.

So, tldr: is there a way to show specific image sizes for the thumbnails on the “Add to Gallery” and Media Library screens?

Thanks