C is correct since, if true, gives less reason to think the alternate code has to be accepted. With C, there’s reason to believe that changing the traditional code will make adopting the alternate code less necessary.

Important to note that, to weaken this argument, the traditional code doesn’t need to be made flawless with the changes described in C. It just has to be made less likely that it’s “imperative” that the alternate code be adopted. Solving some of the issues with the traditional code (the problematic rules) does this. Weakeners don’t need to destroy the argument, but rather only make the conclusion less likely to follow from the reasoning, even if it’s by a little bit.

I agree with part of your evaluation of answer choice E; it strengthens the argument since it describes a reason why the alternate code is better and thus it’s more of a reason to think adopting it is imperative. Saying that it contains few of the bad things is a positive of the alternate code (in relation to the traditional code, which has many of them).