Dual purpose bikes are indeed harder to approach - the 1200GS Adventure I own is a huge tall and bulky machine. It took me a long time to get into them, and I started out with the smaller 650 GS series. They are however remarkably easy to ride, and to do so in almost any condition. They make great commuter bikes as you are much higher and generally have great luggage capacity and robustness for the occasional spill. However you are essentially right - they are not as good as a pure-purpose bike for a particular application. You can dial in your degree of off and on roadability. KTM does the best hard core adventure series, while take your pick for the soft roaders of dubious merit. If you do get into it then BMW run excellent (though rare) off road courses. We all had our bikes, mine a 1200GS, fully airborne on several occasion on my course. And there's a really scary photo from that same course on my eponymous blog header.