That's not true. If it were that easy the builds would be quicker. My last project was 2 hours clean build on CI. I spent a week optimising it and got it down to 90 minutes, and within 2 months it was back up to to 2 hours again. Entropy is real!

Eternal vigilance is the price of a fast build!

Ingo Molnar spent a year trying to improve build times for the Linux kernel [0]

And that was for C, which is relatively straightforward compared to c++.

I suspect it would take months to sort out the project I am on now, and even then full builds would still be slow.

To suggest it could be fixed in hours is ignorance.

0: https://lore.kernel.org/lkml/YdIfz+LMewetSaEB@gmail.com/T/#u