Two things I'd check first:

1. The benchmarks make servers generate a huge number of objects, so maybe, the GC is under too much pressure.

2. Another possibility is that the v8 JIT can't optimize some JS code in nodejs, or does a poor job.

That said, only careful profiling can answer your question :)

C Python uses ref counting, whereas Node/V8 uses GC. Ref counting schemes generally use much less memory and GC scans can be expensive when there's a lot of new data, as is the case for a web server.

How about clustering the Node server? By default, node uses only one process. Making the server use all available processes requires a bit more work (see https://nodejs.org/docs/latest/api/cluster.html or https://github.com/Unitech/pm2) but will probably do more justice to Node.js vs Python.