Or is it that the victims pest warning system is currently winning the biological arms race, in which case how are mosquitoes able to successfully reproduce? Or is it that mosquitoes have evolved such that their spawning numbers offset the difficulty they have biting?
Biology is hard.
It would need to be us that needs to evolve away from being sensitive to mosquito saliva. But our immune system went the other way to be allergic to it so we could defend against any infection or disease the bug might carry. Further proof of human stupidity in our evolution, that we trigger the defense mechanism after the the attack instead of preventing it.