If there is a setting in Discourse that blocks someone from replying more than 3 times in succession quickly it’s there to block spammers. There is no reason for doing what you are doing. Just put all the images in one post and be done. This is an Enterprise level Amazon instance with plenty of power to do what you are requiring. Heck people are uploading 10+ high res images (2+Mb) at one time and you are doing small to medium (300kb) images.
Also you may have missed it but I posted a topic about ways to exclude or mute specific forums/categories that you aren’t interested in. KitMaker Discourse Tutorials