The pharmaceutical company had projected that its new drug would face little competition for at least five years after launch, based on…

The second sentence describes an outcome that replaced the original projection instead of fulfilling it, a much faster competitive threat arriving through an unanticipated production method. Instead signals exactly that kind of substitution: what actually happened in place of what was expected. Consistent with this would incorrectly suggest the rapid competition matched the original five-year projection. For example would frame the second sentence as an illustration of the first's claim, not a reversal of it. Similarly would suggest agreement between projection and outcome, but the sentence describes a sharp divergence.