A lot of the GPU drivers back then sucked since it was a rather large departure from how stuff worked under XP.
Like in one release we went from a model where only a single app could use the 3D bits of the GPU at once, to the system itself using relying on them to present the UI and letting multiple apps share it at the same time.
Not to the same extent, part of the point of AT is that everything shares the same feed, while the AP relays only offer the view of co-operating servers.
Now Mastodon does offer its own streaming API that lets you see every post on a given server, and at least the fedibuzz relay offers that as well, so if you use that API endpoint you’ll see every post of every server it knows about in real time.