I think there is no doubt that the technology for producing dry yeast has advanced. This is true even for bread yeast. Dry yeast once contained large numbers of dead cells (in part in a protective shell, intentionally) and was likely to be contaminated. The dry yeast today is purer and more viable, and I know of breweries that use dry yeast. But in my experience, dry yeast still has major drawbacks. The lag time is very long, giving opportunity for infection. Rehydration also provides this opportunity, whereas in propagating a liquid culture, the culture yeast can establish itself quickly. And it must be noted that yeasts somehow can change in drying: dry yeast from the same source as a well known liquid culture may behave quite differently. I don't know the explanation for this, but a prime example is that the dry version of W-34/70 bears little resemblance to the real thing, though it is genetically true. But if a dry yeast works to your satisfaction, ignore outdated warnings and use it.