I have the original CY 21/2.8, and am familiar with the WATE only from the terrific images and MTF. They are surprisingly similar, the kind of lenses that makers like Canon and Nikon would reject, most likely.
I think of these Distagons as very high impact lenses - photographic lenses - so if low/no distortion and antiseptic performance is desirable, look elsewhere! Canon's TSE series and the 14-24/2.8 Nikkor will suit that buyer class much better.
The WATE is better at wider FLs than at 21mm, has a little more vignetting at same apertures, so the 21/2.8 handily betters it in corners, in particular - at 21mm. Both have moustache distortion - love it or hate it, me I love it and seldom correct it, as corner definition matters more - but the WATE concentrates its heavy distortion at wider FLs, and by 21mm it's down to 1.5%, where the 21/2.8 has 2.5% with a bigger kick up at far corners. Both are super contrast, so the new high dynamic range sensors suit them to a T.
As with the new Distagon 15/2.8 (also a terrific lens) the 21/2.8 is excellent at the f2.8 stop the WATE cannot make. This is true particularly for the later 'warmed over' 21/2.8 in ZE/F form - Zeiss are now concentrating harder on both close focus and wider aperture performance than they formerly did. The Zeiss at f4 is substantially better everywhere in the frame than the WATE, with that biting micro-contrast the lens is famous for. It seems to tear away at the subject at times - the epitome of the Zeiss look. It's also a low 'focus mistake' lens because OOF is so well managed - just a whisker off infinity and it all looks fine.
The CY version is 530 grams; the ZF version is 600 grams, the ZE version is 720 grams; the WATE is a mere 335 grams, and much smaller and shorter. All this is important for the a7/r as you will be adding the adapter weight and bulk.
Note also that Zeiss will up the ante soon with new WAs, reportedly in 24/2 and 21/2.8 form, with the 24/2 first up:
Sony E and FE Lenses | Sans Mirror — mirrorless, interchangeable lens cameras | Thom Hogan
Their last three FF lenses in manual focus are the 135/2 APO Sonnar, the Distagon 15/2.8 and the Otus. What will they do for FE? Thousands will be watching. Especially Leica M folks ;-)