That sounds good in theory, but it really doesn't work out in practice. If you want a like-for-like comparison, you end up with similar weights.
The Olympus OM-D E-M1X comes in at 850g for the body alone, which puts it squarely between the Canon R3 (~1kg) and the Sony a1 (~750g). Once you adjust for the equivalent light-gathering ability of the whole kit , the Panasonic Leica 200mm f/2.8 is 1245g, versus the Canon 400mm f/5.6's 1250g.
The Olympus OM-D E-M1X comes in at 850g for the body alone, which puts it squarely between the Canon R3 (~1kg) and the Sony a1 (~750g). Once you adjust for the equivalent light-gathering ability of the whole kit , the Panasonic Leica 200mm f/2.8 is 1245g, versus the Canon 400mm f/5.6's 1250g.