Chat is not a multi-billion dollar company.
Video conferencing is not a multi-billion dollar company.
File hosting is not a multi-billion dollar company.
The company that does all three of these things in an integrated fashion is. No single feature constitutes a platform or ecosystem, and there's certainly no defensive moat.
These single-purpose companies are just minnows to the bigger fish that have gargantuan budgets, extensive engineering headcount, and rich product ecosystems to pair these features with.