They're not directly solving the same problem. MCP is for exposing tools, such as reading files. a2a is for agents to talk to other agents to collaborate.

MCP servers can expose tools that are agents, but don't have to, and usually don't.

That being said, I can't say I've come across an actual implementation of a2a outside of press releases...

I think they have different use cases. MCP is for tool calling, A2A for agents communicating between themselves.