I have had quite a bit of time with the lens now. I don't think it's character is about specific build quality. It works great as a video lens because it slightly crops the corners. As a stills lens, the corners are stretched dramatically in distortion. It may be just a limitation of the focal length, but the Rokinon 14mm I sold to partially pay for this lens was better in the far corners. Of course comparing a zoom to a fixed lens isn't fair. As for "sharpness", the lens does appear to be very "sharp". There is great contrast and wonderful edge sharpness, but the micro details are missing compared to other lenses I've experienced. So for video it works very well, but not quite what I had hoped. For comparison, an old 20mm 2.8 Minolta AF feels sharper. All things said and done, often more is said than done!
You should not really expect a UW zoom on a UW prime level, A UW prime will almost always have better extreme corners, it will always have less distortion and if you correct it will obviously have less effect. The GM14 vs every lens covering 14mm show the same thing compared to every zoom covering that range better extreme corners and less distortion.
In zooms where it needs to cover more range there will always be some compromises in corner sharpness and there will always be some slight differences across the range also there bound to be more distortion then a prime, this is even true with 24-70GM ii and 70-200 GM ii, in the latter it just benefit for covering a range that is some of the easiest to make tac sharp, why 70-200mm are generally the sharpest zooms and why the difference are less pronounced then the other but even then a GM135 and Samyang 135 obviously have better corners if you investigate it. Tele range is probably the only range where you can truly say about any zoom it’s like carrying a bunch of primes.
In regards to 24GM and 35GM these are noticeable better then the GM 24-70 ii especially in corners, you can also find other cheaper primes where that will be true, the difference I seem between the GM 24-70 ii and the 16-35 G PZ are very, very minor and probably not something you ever going to notice in print.
The Pz 16-35 is sharp for what it is a zoom covering UW and W range, also lenses are bound to be noticeable distorted at 16-20mm range.
The 20G is also noticeable better then 14-24 Art, GM16-35, GM12-24 at 20mm if you want the best performance primes are unrivalled well at least until you hit the 70-200mm GM ii.
That said stop them down and much of primes advantage starts fading at f8-11 where you typically shoot things like landscape it’s generally not huge difference and you will find it hard to pick the odd one out in triangular test in print. You mostly see the difference because you massively pixel peep and even that isn’t without problems as making a reliable sharpness test isn’t without issues. Why we always should back up with lab test as difference sometimes is down to user error or bad luck in terms of a below average copy.
