100 times this. Few years ago I personally edited Makefiles in one HPC project to test GCC and clang as possible replacements for PGI. Lemme tell you this: they were joke. Like, 2x slower.
First of all, commercial Fortran compilers can do all the simple optimizations like inlining, loop unrolling etc. And then on top of that, they come with loads of HPC-specific optimizations like autovectorization, loop tiling, loop fusion and hell knows what else. GCC recently seems to be developing in this direction, maybe they'll become competitive at some point or maybe already are, clang was behind GCC last time checked.
In any case, state of the art Fortran compilers are good. And guess what, GCC has a Fortran frontend too. No need to speculate, you can go and test GCC on your codebase now.
In fact, most modern high performance compilers, open source or commercial, have multiple frontends for multiple languages, usually including C and Fortran.
I think you completely fail to realize that Fortran does have wide adoption, and that there is a big market for commercial and open-source Fortran compilers, and that these optimizations have already been made.
I also don't think you realize how much more productive a scientist is with a language that explicitly lacks all the bells and whistles of e.g. C++. Just like how many fiction authors prefer to use old and simple text editing software, hell even mechanical typewriters, while you would argue an iPad with keyboard cover has so much more functionality.
If you want some examples, go have a dig through the OpenFOAM C++ source code [1], and compare it to e.g. the Pencil Fortran code [2]. They're both CFD codes, though the specializations are different. The former can best be characterized as "templates all the way down", throwing you 800-line error messages when you miss a semicolon, while the latter is downright pleasant to install, use, understand and debug in comparison.
[1] https://github.com/OpenFOAM/OpenFOAM-dev
[2] https://github.com/pencil-code/pencil-code