How fast can you build new aircraft? First day of the war

Howdy folks

I have a question that has been percolating about in my loaf. I’ve heard it said that these days, you fight with the military you have on Day 1 of the war. It takes so long to develop and build combat aircraft that you cannot really rely on recapitalizing your air force during the war.

I was wondering how true this is? For example, in World War 2 the United States built 300,000 aircraft. In 1944, the United States built over 12,000 fighter aircraft. By contrast, a modern fighter production like that of the Rafale produces a couple a month. I realise that this is partly because in peacetime we obviously need fewer aircraft, and also because modern aircraft are in a different universe in terms of sophistication of the avionics, the quality of the parts, and so on.

So my question is, if theoretically we did get into a conventional war requiring new aircraft, how quickly could we tool up to build new aircraft? Do you think that for the purposes of building quickly and efficiently, we might build simpler and less sophisticated aircraft that could be put together more rapidly (for example, if you were to build AirLand Textron Scorpions and load a Helmet Mounted Display and HOBS missiles on them, they could certainly provide some capability).

What do you think?