A YashicaMat (pre 124) weighs just over 1100g. A C33 with 80mm lens is around 2170g, and the Mamiya 6 with 75mm is about 1140g. The full comparison table is at http://grahampatterson.home.comcast....tml#Heading141
Weight is not the whole story. TLRs are basic boxes, and balance well, especially on a neck strap at waist height. The Mamiya C series need a very different grip to handle them, and are probably not the easiest to hand hold. The mass of the camera does absorb some vibration, though. The Mamiya 6 rangefinder holds well, but the eye-level position makes handholding a little less stable.
In many ways the nice thing about a TLR (except perhaps the Mamiya C) is that you don't get tempted to carry a lot of extra bits. My closeup lens set, a couple of filters, and a lens hood live in cases on the camera strap. Add film and a lightmeter and I'm off. No need to debate about needing a long or wide lens.