Looking at the proposal in question [0], it seems very sad that the alternate, not recommended, choice was made instead [1] , especially since the reasoning seems to have not been put down in writing anywhere. The paper does mention that the difference in performance was <4%, with both improvements and worsening being seen by the VC++ implementers.

[0] http://open-std.org/JTC1/SC22/WG21/docs/papers/2016/p0145r3....

[1] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p040...