I'd argue the account given in the blog post disagrees with what you're saying. Up until recently the OS did exactly what the OP wanted:

> I rely heavily on writing on handouts from my iPad, projected via AirPlay to an external screen that my students can see. When I’m doing this, my iPad is also doing many other things: controlling a PowerPoint presentation on my Mac, showing me notes that I’ve taken on points I want to mention and students I want to call on, and showing me the results of polls before I reveal them to the class.

That's not a crippled OS. And he's using it professionally so "Pro" doesn't seem inappropriate. The way the author describes what they're doing, it's difficult to see a laptop replacing it.