Hive is like a Swiss knife, as you said, but also has its blogging and rewards core that can be attached to any project that is attempted on Hive. You mentioned about Splinterlands and their communications directly on-chain, but pretty much every (or 99%) of the projects that take off on Hive use its blogging platform. As much as some people think blogging is old-fashioned, I bet most other chains would love to have this component available in their ecosystem, instead of using external apps.
This blogging aspect is so powerful in my opinion. Not only you can do all the communication on chain with the same usernames and wallets, you can also incentivise people in many different ways!