I remind you that the belief you are defending is that an increase in the number of bugs produced per some unit of implementation "implies that testing and validation has gotten worse", not the general idea that you can or should improve software quality by improving testing and validation.

If we adopt the realistic perspective that the testing and validation process can only catch some fraction of bugs, then an increase in the number of bugs produced in the implementation stage is bad irrespective of what that fraction is. You can improve the testing and validation process so as to minimize the fraction of bugs that get past QA, but when you multiply that by the number of bugs produced in implementation you will be worse off if you produce 7 bugs per month during implementation than if you produce 5 bugs, regardless of whether you can also improve the testing and validation process. You will on average, over time, have fewer bugs in production if you produce fewer bugs during implementation given any testing and validation process that isn't completely fool proof.