AIM would spawn a new window for each conversation. That hardly seems like the pinnacle. Pidgin, with interop with a ton of protocols was superior, and was also an amalgam integrating numerous chat networks.
I see your pidgin and raise you an "interoperability." Pidgin was a thing because the chat protocols/servers were open interfaces. Gone are those days. I miss being able to use different clients for chat.
Having been subjected to every Microsoft chat application since 2000, I can assure you that each one started worse than AIM and got progressively worse.
The only exception was driven by my employer, who opted to embed Cisco Call Manager crap into Microsoft OCS (the circa 2010 chat client). I would rather communicate via requisition notes in peoplesoft than use that shit. Whatever replaced it (iirc Lync for Enterprise Business Extreme Edition) was better.