Yes, Zuck tries to destroy Snapchhat but close to it? No way. Slowing their growth? Yes and this was expected.
Instagram is winning this space? IDK, I only know that Instagram ads perform 10x worse than FB ads. After many test drives I've never touched them again. The only ones who are monetizing on Instagram are those shiny influencers. Paired with the current brand dillution (glossy Instagram vs not so glossy stories) I am not so sure about Instagram's long-term success.
Snapchat has still a much better feature set plus much higher stickiness with direct messaging than Instagram plus a consistent DNA. Finally, Instagram has many, many liking bots (feels like Twitter before the fall).
BTW, stories only work on Instagram while on Meesenger and the FB app they are not used by anyone (at least in my cricles).