I'm always a bit skeptical when I see differences of more than a factor 2 when looking at benchmarks. In reality most frameworks are pretty close in performance with the exception of edge cases around specific functionality.
I think that your specific 3-6x slower figure is coming from the way you manage your lifecycle.
https://github.com/ppanyukov/EntityFrameworkBenchmarks/blob/master/src/EntityFrameworkBenchmarks/Startup.cs#L22-L29
You are using a completely different type of lifecycle (transient vs singleton) for EF and dapper. This means (amongst other things) you are creating a new connection when querying EF and reusing the connection with dapper.