I would argue in the following way: It is an optimization problem, NP-hard. It does not matter how much faster another language would be, since this only adds a constant factor to the running time - is that true?
One way to answer the question would be to benchmark it against an implementation in a "good" language (your terms, not mine) and see how much of a difference it makes.
I don't buy the visualization argument. If your "good" language implementation was communicating with a front end you might be able to have faster performance and visualization. You might be overstating the cost of communication to make yourself feel better.
With that said, I'd wonder if it's possible to treat this question fairly in a forum like this. It could lead to a lot of back and forth and argument.
Are you seeking a justification for your views or do you want alternatives? It's hard to tell.
See especially his demo of JS creating a scene graph:
Here is my screencast of the demo. Alas, since RiverTrail currently targets the CPU and its short vector unit (SSE4), and my screencast software uses the same parallel hardware, the frame rate is not what it should be. But not to worry, we’re working on GPU targeting too.
At CapitolJS and without ScreenFlow running, I saw frame rates above 35 for the Parallel demo, compared to 3 or 2 for Sequential.
The only way to answer this question is to measure and evaluate those measurements as every problem and application has different needs. There is no absolute answer that covers all situations.