I feel like it would be better to have a dedicated Reddit-mirror instance that instances can choose to federate with.
The issue is mirror posts are not organic which is not conducive to high quality discussion. If a community only gets 10 original posts a day but a mirror bot is dumping well over 1000 posts a day, that's a problem because the organic content will get drowned out and further disincentivize people from posting and actually growing the community.