Yeah. OS X will kill the device. Not only is it not optimised for the touchscreen interface and has to have all sorts of programs to be optimised for it as well, but it is a complete hog. Imagine that they filled this iPad Pro to the brim with general good stuff.
For example, 13000mAh battery, up to 256GB of storage, and 4GB memory. These sorts of specs will make the iOS running iPad a powerhouse. But slap OS X onto this thing, and your battery life will be cut short by a significant amount, you would not be able to do any pro work without running out of memory, and you would be careful about running out of storage. Bear in mind that this is somebody who has used OS X for no longer than a week, but this is just the general idea I get. Maybe some of this is in part due to the architectural differences, but I'm no expert on that.

should really just work on getting iOS up to the standard of OS X without sacrificing efficiency.
Sorry for the long winded explanation.