Companies fight, users lose. Same story, different day.
The press nearly always gets this wrong and the viewpoint has taken root in our collective thinking.
Competition is about customers, not competitors. With competition, customers should get better stuff, more stuff and cheaper stuff.
I've seen very little "users losing" in the past 10 years, despite continuous reporting to the contrary. Were this not the case, we wouldn't even have a twitter, facebook or instagram - we'd all be using the same thing provided by the same company and it would most definitely be outmoded and suck.
Competition works. Get used to it, change sucks.
When companies "compete" by buying out the competition and shutting down trade, there is a loss of choice and utility and a loss to consumers.
(granted, this is a simplistic view and subject to the whims of regulatory distortion and other externalities - I think my core premise is sound though. Even though these specific companies might be limiting options that just creates more opportunity for competition and stronger benefits for customers...)
To take an example relevant to the OP, what about Twitter shutting down third party clients? How was that a win for the user?
Who are FaceBook's and Twitter's customers? Certainly not the users. So it's still possible that users lose.