Question about the performance of method calls

Hello,
I am trying to improve performance of the QML scripts in my app.

While looking at traces, there is something that seems pretty weird to me.
I have the following code in QML:

      for(let s = 0; s < n; s++) {
        let sample =  /* some small computation, e.g. Math.sin */;
        out1.setSample(0, s, sample);
        out1.setSample(1, s, sample);
      }

out1 is a C++ QObject with the following slot:

    void setSample(int i, int j, double v)
    {
      // c is a std::vector<std::vector<double>>
      c[i][j] = v;
    }

when I look at the trace, I notice that every time setSample is called, there's a loong call to QV4::QObjectMethod::create which seems to do a lot of stuff, and allocate a lot of memory.
Like, all in all, my actual c++ method call, visible at the left (JS::AudioOutlet::...) is 1% of the total of the call... and I'm in a debug build !

Is this 100x performance penalty a fact of life of QML which cannot be avoided ? Is there some missed optimization / caching opportunity lost here ? (e.g. I'd assume something like a per-metaobject method cache?)