I don't know about you, but I consider the 2.5 pound difference in your example here to be rather large.
That said, your listed ETRSi setup is pretty much a worst case scenario. Going with the manual speed grip instead of the motorwinder will save a fair amount of weight (and personally, I prefer thumb winding to motorwinding, so that's a double win in my books). Replacing the zoom for a single prime will make a huge difference (of course you lose the felxibility, but then, I enjoy selecting a single lens for my day/task and sticking to it). And depending on personal usage style you can replace the AE prism for a WLF for another big weight savings.
My setup is ETR-Si, 75mm F2.8 PE, AEII prism, speed grip, and 120 back. It comes in somewhere around 4 pounds (I haven't weighed it). It's remarkably close to my Dad's D80 w/18-200 lens though. Definitely a huge weight difference compared to my OM40 w/nifty-fifty, but still doable. I'm hoping to get a WLF for a really street friendly setup.
Our work here is done. Check back in when you need somebody to talk you into LF and ULF though. :-)
Don't even joke about that, I spent 3 hrs looking at baby Graflexes because, hey, cheap MF!
Then, looked at 4x5, cause Weegee...
Then though, hmm, I could always load up some 4x5 in my changing tent
JUST NO! Not yet!
It's a very nice set and the price is very reasonable. It enables you to go light & small with the waist level finder and the hand crank. Or go bigger, larger but more convenient with the metered prism and the winder. Even then it still fits in a smaller camera bag. I had a (non-TL) Pro with the prism, winder and a 2.8 150mm lens with me on a stroll through old Montreal last Sunday with my wife and 4yo daughter. Weight & size was not an issue. I saw a gentleman with a Mamiya 7 II on Place Jacques Cartier and his camera bag was way bigger than mine. Forgot to ask "Is that a Hasselblad".