Getting hung up on the difference between a mirror and a relay is moot. I don't see how people would be more accepting of that. In fact it seems like more people would object to having their posts mirrored to reddit considering the reason many are here is to stop participating on Reddit.

And it doesn't eliminate the initial problem which is that the posts will be considered spam by the largest instances.

So you could not care and do it yourself, but I suspect that it will result in the same reduction in community engagement as the prior attempt.