You have part of the idea right. However you have to consider that evolutionary pressure works with regards to competition for resources. So yes a drug-resista

You have part of the idea right. However you have to consider that evolutionary pressure works with regards to competition for resources. So yes a drug-resistant bacteria might be outcompeted for limited resources in a normal environment by bacteria without that adaptation. However, if there is an antibiotic introduced into the environment, the drug-resistant bacteria will probably have proportionally more resources than the non-adapted bacteria did before the drug was introduced, due to a complete elimination of their competition. This is assuming that the adaptations bacteria have that enables them to be drug resistant harm their fitness in a drug-free environment in the first place. It is entirely possible that the drug was targeting a trait that actually required more resources to produce, but that wasn't selected against because it was basically vestigial. I think it's a pretty big misconception that the force of natural selection is directed towards absolute efficiency. I'd classify the process of natural selection as a 'good enough' mechanism.