Maybe you should tell the Linux developers that they are making a mistake.

Even assuming the 5% number were correct (depending on how expansive your optimisations with UB assumptions are, it may not be), asking everyone who doesn't adjust their compiler flags to accept their programs being silently miscompiled for some theoretical benefits is at odds with economic reality.

Times like this I wish I were allowed to say exactly how much money a 1% fleet-wide loss in performance costs a big tech company.

A) there is no evidence such phenomena - especially in net- are due to unsafe optimizations, b) those companies dont need to shift their costs to other users