A dream come true for many landscape shooters & travelers. A7r + FE 16-35mm f4 OS = light weight package with a full pocket of spare batteries.
Anyways, Canon 16-35 f4 IS is a GREAT lens.
Noboby said the Canon is not a great lens, it's likely the best of all 3, and I will probably get one in a near future.
However I am not sure I get your point about the A7r combo :
Canon 5D3 (905g) +16-35 L IS (615g) + 2 LP-E6 (about 150g) = 1715g
Sony A7r (407g) + 16-35 ZA (518g) + let's say 5 NP-FW50 batteries, to make it balanced (215g) = 1140g
When you go for landscape / travelling, it's very likely you carry at least a small backpack, so carry 3 more batteries is not really an issue (except for the cost) since the Sony batteries are about half the weight of the Canon ones. On the other hand 575g total weight less is not subjective when hiking / travelling. IMHO, for landscape / travel / architecture (and I am NOT saying for sports, birding, weddings or whatever else), the Sony combo wins, especially when you take in account the sensor low ISO capabilities (although for travel some might not want the extra resolution).
Well, I think it is OK when better = heavier and more expensive.
What's wrong with adapting Canon EF 16-35/4L IS on Sony A7r?
Battery life is like Canon 1 : 3 Sony, and for a landscaping trip you may end up with 10 or 12 NP-FW50, because battery life in landscape photography is not about the number of shots you take, but the amount of time you are waiting for the right moment and unlike DSLR you can't even work on the composition with your A7r being turned off or in standby mode like most DSLRs are most of the time.