There can be no doubt that moving to a m43 system can lead to a very significant reduction in the weight that you will be carrying, particularly if you need a wide range of focal lengths. At longer focal lengths the weight advantage is very significant indeed.
By way of an example the Canon 100-400mm weighs in at a hefty 1,700g compared with just 1,000g for the Pana Leica equivalent. On a crop body the Canon lens gives a full frame equivalent range of 160-640mm whereas the Pana Leica gives a more useful 200-800mm and despite first impressions is in effect no slower than the Canon.
To get to 800mm the with Canon requires the 500mm, which whilst a fabulous lens, and I have no expectations that the Pana Leica 100-400mm will match this lens for quality, is of course extremely heavy, bulky and very difficult to travel with.
Overall this “core” wildlife & landscape kit in Lumix Pana Leica form weighs just 24% of my Canon kit – a saving of circa 6.3kg.
Canon: 5D mk3 & 7D mk2 16-35 f/2.8 – 24-70 f/2.8 – 70-200 f/4 – 100-400 f/4-f/5.6 – 500 f/4 = 8.6kg
Panasonic: Lumix G9 – 8-18 f/2.8-f/4 – 12-60 f/2.8-f/4 – 100-400 f/4-f/6.3 = 2.3kg