Perhaps so, but they already covered that scenario with an earlier limitation on AP/YD use during take-off, landing, and OEI operation.
If they really wanted to make it impossible to enable the YD without the AP and vice-versa, then they should've disconnected the YD button on the panel.
I wonder if it's just a poorly-worded restriction where they meant to say "don't use the AP without the YD," but only Diamond can speak to the intent and provide any reasoning behind it. Until then I guess we're stuck with it as a limitation.
I inadvertantly landed with the YD engaged once during ME training, and it was not fun. I don't remember the sequence that got me into that state, but I make sure to check for it now.