My Mamiya 645 Pro TL with back and AE prism weighs 1.4kg.
Add 500g for WG401 power grip with batteries - I don't use it often.
Add another 500g for 80mm F1.9 or 200g for 55mm F2.8.

In comparison, my EOS 3 with power grip weighs 1.5kg. And my EF lenses weigh more than Mamiya Sekors.