Yes, or becoming a competitor, signalled by having users and getting more. "Strategic" aquisitions often seem absurdly high, unless seen as a threat to the future of the acquirer. You can be a threat without being fundamentally new.
I guess the only way it could happen is if it didn't look like a threat until far too late, such as totally different customers (e.g. third world), doing something completely different and no where near as good (e.g. markdown a threat to Word; iOS/android vs Windows)
Of course you are. Just reject the offer. You don't think Uber/AirBnB/Dropbox etc have received offers we've not heard about?
But stuff like Oculus is bought in its infancy - that is not desire to profit, but to control. FB could have acquired 20-30% of the company to provide them with liquidity.
Not really. Most startups don't want to sell that much equity to a potential partner/acquirer unless they have to.