“Actually” the rate-limiting stuff wasn’t really to do with spam on this site. It was more to suppress support requests. This site was not originally intended to be used for support for Ubuntu products. We have other sites like AskUbuntu and the Ubuntu Forums for that, and they do a much better job - being well-established communities, with many eyeballs and high Google search rank.
When we turn off/down the limits, we’d get people signing up here and asking all manner of support questions (printers, GPU drivers, everything). Even though we had banners that indicated boldly that this is not a support site, people ignore that and would use it for that anyway.
We spent a fair amount of time closing threads, and re-inforcing that rule. The limits suppressed this quite dramatically down to almost zero.
I appreciate that the LXD community discourse was used for support, and thus migrating that community here will have some friction due to these conflicting requirements of discourse. I would recommend that the powers that be (not me, as I left Canonical a couple of years ago) think this through carefully. Otherwise, you’ll get not only well-intentioned LXD support tickets here, but also Ubuntu and all other Canonical product support requests here. Without the eyeballs/community to answer them.
Just my 2p