I think he's spot-on when he says that when we talk about "what the Buddha said", it can only refer to specific textual representations of a character called "the Buddha", and it is not really possible to trace any of these back with any certainty to the historical Buddha. So he is really saying "one of the Buddha literary characters is an astute businessman." I don't see how anyone could argue with this simple fact. Fortunately, the validity of the ideas in the texts is not dependent on proving their origin, and even the Buddha (or at least some of the Buddha-characters we see represented) would agree. "Whether Tathagatas arise or not, the dharma is the dharma." In Christianity, the person of Christ is paramount and because the historicity of the gospels cannot be seriously entertained, the whole edifice arguably collapses. Buddhism does not have this problem, since the information is experientially verifiable without the source being essential. Christianity is the messenger more than the message. Buddhism (especially in its Sutric form) is the message, not the messenger.
Schopen is an historian, and is therefore speaking of Buddhism as an historical & cultural phenomena. His evidence is limited to texts, inscriptions and archeological findings, as he would himself readily admit. Within these parameters, what he is saying is fairly uncontroversial. He is making no claims about the soteriological or veridical status of Buddhist doctrine, indeed I don't think he cares about those questions at all. This is a certain type of secular scholarship applied to, in this case, a religion, and it can provide interesting information as far as it goes, but can, I think, also keep people from living in a la-la fantasy land thinking that any text that is presented as a sutra actually is the actual words of the actual historical Buddha. Closed-minded religious fundamentalism is not only found in the Christian and Islamic traditions.
Look, a religion can present itself as myth, in which case you can take everything that is said as a sign & there is nothing to argue about, or it can pretend to be history, in which case it is subject to historical scrutiny. That historical scrutiny, when honestly carried out, often shows that the so-called history really is myth after all. Which of course is not to say it is any less valuable.
Thoroughly tame your own mind.
This is (possibly) the teaching of Buddha.