A friend of mine is a travel photographer and he has an a7r2 with a couple of primes and it's really light when it's stripped down. It's a really versatile camera.
When i put the big lenses on it it actually becomes too front heavy, so i end up using the battery grip to balance it out a bit. But for me it was more about the image i produces than the overall feel of it. I'm happy with my investments, i do miss the canon's sometimes, but i don't think i could ever switch back now.
Yeh thinking of the Sony a7r2. I think they are good for videos as well but i think battery drains real quick. Will probably buy 2 extra battery pack whenever i purchase it.
Carrying my canon 80d with a 17-50 zoom was tiring as hell. My d600 with a fifty is a little better.
I guess for pros, quality image is everything. As for me, i think comfort takes priority. When ur happy, stick to it. I started with Nikon then tried Canon, switched to Nikon coz I liked the layout more. Each to their own.