I'm not sure I follow your reasoning. AIM could have created a great mobile app with new features a la whatsapp et al, a new OSCAR protocol that was backwards compatible, and had a huge base of mobile users.
Hindsight is 20/20, but it sounds like you're saying that even with hindsight closing AIM was the right call.
It was the right call. AIM was losing money with no obvious way to monetize it. AOL was not in the same position than Microsoft was. They had little experience selling to pro customers and they were bleeding users to Google Talk and Facebook Messenger at the time.
Even knowing that the mobile market would explose in popularity, it is far from obvious that AIM would have even been positionned to benefit from it. Google Talk was really popular then and notoriously failed to convert that into a leading position in the mobile market.
it was basically explicit transfer of the core value - user graph - from AOL to FB which probably doubled or tripled the FB graph at the time. The "small deal" and the modest "linked" below are kind of euphemisms describing the full buddies list import and thus sucking AIM dry if i remember correctly:
https://marker.medium.com/the-untold-history-of-facebooks-mo...
"During his time there, AOL wound up doing a small deal with Facebook that linked AOL Instant Messenger to Facebook’s website. But the biggest outcome of the deal was the connection Palihapitiya formed with Mark Zuckerberg."
So the GP{3} saying "short sightedness and pettiness of these directors is something of legend" is very wrong. As you can see they played very long and successful game, just not the game you'd have expected them to play :)