Let's say that C produces 100% of the performance available. How much does Go produce? Maybe 90%? How much does Python, say, produce? 25%? So going from Python to a compiled language produces a huge gain, and going from Go to C produces a little bit more.
But why not get all the gain? Well, sure, if performance is the only thing you care about. But it usually isn't. You might also care about networking, or multithreading. Would I rather write that code in C, or in Go? Is it enough better in Go to be worth that last 10% of performance? Arguably, yes.
When someone says "X matters", it doesn't mean that they are saying "X is the only thing that matters". It is not correct to conclude that they should, for consistency, be saying "turn the X knob as far as you can". Instead, interpret it as saying "given your other constraints, look for a sweet spot where X is somewhat toward this end of its range."
Yes, that's my point. It is premature optimization, because you do not have a use case for such performance. Instead you might want Python's extensive numerical libraries, or you enjoy its quick prototyping capacities. The same way that you do not always go for C, and sometimes prefer Go, because of non performance related requirements.
That's why saying a compiled performant language should be default is not logic I understand. Default should be whatever you need for your requirements. If you don't need anything special, just go with what you already know well.
Fine, but if that's your point, don't say "Why not use C all the time by default then?" Actually make that point, rather than leaving us all guessing as to what your point is, and more important, why it's your point.
And, as I said, "Why not use C all the time by default then?" does not actually follow as the logical endpoint of the argument that your trying to answer, so making that your response really doesn't contribute much to the advancement of the conversation.