Is the herd effect wrong? This is not a simple question to answer with objective pareto-optimal answers for everyone.
If the promising direction pans out, having 3-5 drugs in the pipeline represents a far faster optimization problem, with far faster discovery, leading to more years of lives saved. Going slow, waiting for one drug to succeed or fail, learning maximally, then maybe trying another, may be dollar optimal, but has other risks: abandoning a good direction too early because of stochastic decision making (see for example the story of GLP-1 agonists which were delayed for decades because of optimizing to avoid me-too diabetes injectables), and also not exploiting a very promising target that pans out well in the first trial.
The speed issue is also one reason that trials are so expensive, and why drug discovery is limited in what we can try. If there were lower barriers to entry for trials--that somehow maintain the same safety characteristics--then perhaps we could learn faster and better and more cheaply. And the quote talks about a very important thing: there's only so many data points we can collect because there's only so many people who can ethically go on to a clinical trial in the first place. How we optimize the best outcome for those clinical trial patients, and the best outcome for society in general from what we learn from the trials, does not have a clear and obvious answer. This is why ethics classes belong in the curriculum of all advanced bio degrees, IMHO!