I agree to a certain extent that
Right thought, wrong idea presentation. The more accurate presentation would have been; "I agree TO the extent that..." since you are representing a degree of agreement. The idea is to present the end of your agreement with the topic. There is no need to represent the reason for your disagreement since you are asked for the measure of your agreement or disagreement. Pick one of the two discussion choices to represent in the essay. This is still a single opinion essay rather than a comparative discussion.
however, I also believe that investing in finding the proper cure is just as important.
You are not being asked to present a solution to a perceived problem in the discussion instruction so this sentence is a total waste of word count and discussion space. It will not receive a score and instead, will lower your TA score due to a change in your discussion slant from the original.
Try to focus on only aspect of the discussion. Since you already agreed that the prevention is more important, then focus on that discussion alone. Do not contradict yourself in the discussion by agreeing with both sides. It is either you agree the cure is more important or the research is more important. Either agree or disagree. Create a clear opinion for yourself of risk being scored based on the lack of a clear, one sided opinion.