Although it may have the same fate, AIM suffers from being computer only when it was in its prime. (maybe always) Anywhere I go I can socialize on whatsapp, or snapchat or whatever app.
I think you're touching on something here. Around the launch of the iPhone (and rise of Androids) many companies that got on the mobile-first bandwagon survived, and those that assumed web-only to be the best way really quickly died.
I don't think it was purely Facebook that killed MySpace and AIM, it's that they didn't get on phones quickly enough.
What made Whatsapp popular is that it worked just like SMS. Users are identified by phone numbers, so you can use your existing contact list.
However unlike SMS it didn't cost eye-watering amounts of money to use. Whatsapp never became popular in the USA because most people on pay-monthly contracts received large SMS allowances.
In the rest of the world, networks felt threatened by SMS -- if texts were too cheap then people would stop making phone calls! So it was universally crippled with ridiculous limits and fees. Even in 2018 it costs me a lot of money to send an SMS, and I don't know anybody under the age of 35 who uses it.
I don't think it was purely Facebook that killed MySpace and AIM, it's that they didn't get on phones quickly enough.