etrotta

Here's a link to the report: https://stacks.stanford.edu/file/druid:vb515nd6874/20230724-fediverse-csam-report.pdf
It is from 2023-07-24, so there's a considerable chance it is not the one you were thinking about?

Their arguments still hold up pretty well as far as I can tell. If anything "improved" since then, you could argue that what the biggest platforms decided to use (Mastodon, Lemmy) became the de-facto dialect in use, but you still have to explicitly refer to how certain projects do things if you want to implement ActivityPub, which can be pretty demotivating for developers, and doesn't makes the user experience any better.

...and nothing prevents new apps such as Threads from using ActivityPub differently, being incompatible with existing apps and further dividing the space

If by algorithms you mean things like GPT, all data on the fediverse is effectively public and arguably even easier to be collected than the likes of reddit, and is almost definitely going to be used to train models whenever or not the fediverse federates with threads.
There's still significance in defederating though, specially when it comes to preventing "Embrace, extend, and extinguish"