The new canon 400 f2.8 IS II is very much lighter than the nikon 400mm.
Yes, you are right.
| Nikon VR | Canon Mark I | Canon Mark II |
300 2.8 | 2900g | 2550g | 2400g |
400 2.8 | 4620g | 5370g | 3850g |
500 4 | 3880g | 3870g | 3190g |
600 4 | 5060g | 5360g | 3920g |