[toni-a]

For me

 

Yes. 16mm are the finishing line for landscapes in my book. 18mm or 20mm are still my preference.

If you ask me I'd say that 90% of the photographers can't handle ultrawides and add 9% for those 10mm.

I find it extremely tough to shoot a really good ultra-wide image - and most of our samples in the relevant reviews don't qualify there.

Agreed here, I am not  an architecture photographer (maybe because I am not good at it) however my trial with architecture says fpr architecture and cityscapes you do need ultrawides maybe 10mm would be enough there. knowing that personally I won't use it and I easily prefer fisheye for such shots, si I  fall between the 9% you were talking about