Why had you turned off uploads? Do you not understand that the default is for Discourse to download the images from Imgur (which is why you’re rate limited) so you’re not saving any disk space by disabling uploads unless you turn off the Download remote images to local site setting?
If you want people to link to images that will no longer be available and leave broken images in your forum, then you should turn off Download remote images to local so that Discourse won’t download the images from Imgur to store locally.