With nearly 1000 oncology drugs in the pipeline, I agree that very few will ultimately emerge as winners but I don't think that necessarily makes investing in oncology focused biotechs a suckers bet. The majority of the biotech's I invest in are pre-revenue so I'm primarily focused on identifying situations where the value of the pipeline isn't reflected in the current share price irregardless of the commercial outcome (which could be 5 or 10 years down the road).
Of course, this makes the handful of companies, like ARIA, who are able to develop and commercialize multiple potential best-in-class oncology compounds all the more valuable.