I used those as examples but I claim that most everything was C by the early 90's. The statement that C compilers got fast which allowed it isn't true. When a new compiler came out it was always a couple of percentage points faster than the old version. Meanwhile hardware was doubling in performance every two years.

C compilers didn't need much optimization because there wasn't much performance that could be optimized into code on the simple CPUs of 1992 when Doom was being written. CPU's weren't the superscalar multi core monsters they are today. A compiler couldn't take advantage of reordering instructions to use multiple adders because there was only one.

Those games didn’t have the splash that Doom did for this sort of thing.

I would say that Wolf3d would certainly count as proof of concept.