Facebook is plenty strong
Facebook has messed up, IMO, plenty of stuff. However, its grasp on how to build a social network is demonstrably good. They do not have any realistic competitor in a space that is clearly important enough to engage a significant percentage of the world's population.
The inability of the mighty Google with its massive resources to make a dent should give you some indication of the resilience of Facebook.
Twitter is not a one-to-one competitor that worries Facebook. If they were, Facebook could easily mount a similar platform and crush them.
Facebook is where it is because of particular network effects that do not apply the same way elsewhere. The network effects in play with Facebook are exceedingly strong.
Facebook has built out an enormous infrastructure that allows them to not only service the current demands of Facebook users but future demands of those users and other users besides. Should they decide to mount a competitor to Twitter, Vine, SnapChat, Pinterest, Tumblr or whatever, they can do so almost overnight.
Given Facebook's resources they should, if they don't have one already, have a 'skunkworks' where they build and test competitors to all those things.
Facebook's big opportunity, which they have not capitalized on yet, is to refine their marketing apparatus such that people are only presented with advertisements for stuff they would be in the market for anyway, to police offers to make sure they are good ones and not a waste of their user's time and to put in place a payment and delivery infrastructure similar to Amazon so that, for instance, around dinner time, someone who is likely to order a Pizza anyway is presented with a good offer for one for delivery and can order it with a couple of clicks.
Facebook needed network growth more than anything else, so they played fast and loose with privacy and data. They are now reaching a point where they should be putting together a model that entirely locks down privacy and data such that except for possibly public postings of pictures, nobody including Facebook themselves, can gain access to private data.
With the correct privacy controls in place, Facebook can attract back followers for whom privacy is an issue. They can create mechanisms that would allow 'cliques' to erect their own barriers and admit their own members, etc.
The network with the critical mass is the only asset that matters. Everything else can be done once you have that. Competing against the network with the critical mass is virtually impossible, no matter the resources you bring to bear. As of now, Facebook owns that network and the only way they will lose it is if they shoot themselves in the foot -- repeatedly. They have not done so yet and appear to be in no danger of doing so any time soon.
Back in 2012, Forbes published an article saying that Facebook (around its IPO) was *no way* worth $75 billion. I wrote an article in response saying that if I had the $75 billion I would put it down in a heartbeat. Had I been allowed the opportunity, that would be worth nearly twice that today. Not a bad return on such an enormous amount of capital. Facebook is valued around $130B+ right now and I still think it will increase in value over the next few years. The network phenomenon that they have in play is quite unlike anything we have seen before.