A 10% speed improvement on 1000's of jobs could in theory save you a nice chunk of time. This becomes very important in the financial market where you need batch jobs to be finished before markets open, or you just want to save 10% on your EC2 bill.
So they definitly don't agree you can do the same with free software.
However, I recently ran the Polyhedron Fortran benchmarks with the compilers to hand (~2020 vintage). XL (on POWER) was the only one that gave a significantly better bottom line; obviously IBM know how to compile Fortran well by now (or by Fortran-H). As far as I remember, that was essentially due to the treatment (vectorization) of maths intrinsics, which probably aren't so dominant in typical HPC code. One bad case -- fmod inlining -- has since been fixed in GCC. Without GCC's unfortunate longstanding failure to vectorize sincos (or equivalent), gfortran should have beaten ifort significantly in the bottom line, and at least got close to XLF. PGI was distinctly worse than GCC, but may do better at OpenACC/GPU offload, for instance. XL may win on OpenMP, since some of the current standard was for Sierra's needs. I should find time for the NAS benchmarks.