> ...how is this relevant?
How is it not? This entire thread is about comparing iOS to a fully unrestricted desktop operating systems where we all work normally.
> Some obscure CAD package is not exactly the litmus test of how usable an iPad can be.
Actually, it is in this case. That was the entire point which was clearly stated from the first sentence:
> The second you want to branch out and try something different...
So the obscure CAD package itself is not the litmus test for how usable something is, no. However trying to use one or more obscure package is the litmus test for how usable the iPad is in its ability to let you branch out and try obscure things.
> Actually there is...
Well that would have really been some relevant information to reply with.
So what's your solution? Running a virtual machine containing a fully unrestricted OS on your iPad? (EDIT: I see someone below pointed out the "Fusion 360" iOS app which seems like a gimped, ahem I mean mobile, version of the full app.)