> The problem is not that companies are able to increase prices and improve their margins. That's good!

That's going a bit too far. Under perfect competition there aren't any profit margins: everything sells at marginal cost. Real-world markets won't be like this, but they can get reasonably close. If there are large and increasing profit margins, that's a sign something has gone wrong.

Also, we need to be realistic about natural monopolies. Sometimes the competition we want isn't in the cards, and treating the symptoms really is the right answer. If that necessary-but-low-volume medication has sharply declining costs with increasing production, as many things do, there just aren't going to be enough suppliers to build a competitive market. Competition policy is great, but it can't do everything.