On the whole I'd agree that most of the time it's better to focus on high-quality up-to-date summaries/textbooks than high-quality classical sources.

But I'd suggest a few caveats:

1) It is much easier to find high-quality classics than it is to find high-quality contemporary stuff. Everyone knows who Darwin was, I don't even know how to find a good biology textbook, and I personally got a lot more out of reading and thinking about Darwin than by reading my high school biology textbook. This is a consideration for students and autodidacts, less so for smart and well-informed teachers who know how to find the good stuff.

2) Many summarizers are simply not as smart as the greats, and don't pick up on a lot of good stuff the classics contain. This is less important for a survey that has only a small amount of time to spend on each topic, but if you want deep understanding of a discipline, you will sometimes have to go beyond the available summaries.

3) The ancients are the closest we have to space aliens; people who live in a genuinely different world with different preconceptions.