It is an alternative. It just doesn't fulfill all the needs Airdrop does. I've had situation where I want to share a photo or a text file and it'll work great in that scenario.

Probably the main "feature" AirDrop has is speed. Other alternatives should include that "feature".

No it isn't? The main feature is sending things peer to peer.

That's not a feature that's a purpose.

So what? Anyway the more important difference is it requires both computers to be on the same LAN. The main point of AirDrop is you can share between two devices with or without LAN, with or without internet.