No you are incorrect. noVNC is still ultimately a client, a simple baked-in static web server does not a PaaS make. Guacamole is a turnkey server that works out of the box where you get a full blown GUI and control panel and everything. Guacamole has the added overhead of the proxy but it's a lot more convenient. Unless you are doing high performance applications like cloud gaming with the server halfway across the globe, Guacamole is more than sufficient if you don't want to fiddle with too many knobs.
As a user of noVNC, I'd be interested in such comparison, too. I haven't used Guacamole, but as I understand, sansnomme's point is that Guacamole compared to noVNC is like Visual Studio compared to GCC - while GCC and noVNC offer you most basic tool, Guacamole and Visual Studio provide some helper utilities around - like session management, config UI, etc.
So when compiling single-file "hello world" app or connecting to a single machine you would prefer a simpler tool (GCC/noVNC), since more complex tools require more complex workflow; but for more complex projects (or when you have tens of machines under your control) you would prefer more complex tools.
Disclaimer: I have never used Guacamole, used Visual Studio very little, and my experience with GCC is rather limited.
