Since the landscapers usually stop down to kingdom come, f/4 (especially since it's f/4 on FF so "true" f/4 yadda yadda....) isn't going to bother them a lot.
My trinity set on Canon now is all f/3.5 or narrower (16-35/4, 24-85/3.5-4.5, 100-400/4.5-5.6) and it doesn't really bother me, when I need something drastically faster I have the 24/50 primes. In most cases, f/2.8 vs. f/4 is not a life saver anyway so I don't fret about my 16-35 not being faster (I had the f/2.8 L II... it went right to the chopping block after the f/4 hit the market). My main long lens is the 70-200/2.8L IS but it's in the sickbay for now, and the 100-400 does well.
(I do landscapes but I'm not earning my living from that, though, so take this with a grain of salt).
My trinity set on Canon now is all f/3.5 or narrower (16-35/4, 24-85/3.5-4.5, 100-400/4.5-5.6) and it doesn't really bother me, when I need something drastically faster I have the 24/50 primes. In most cases, f/2.8 vs. f/4 is not a life saver anyway so I don't fret about my 16-35 not being faster (I had the f/2.8 L II... it went right to the chopping block after the f/4 hit the market). My main long lens is the 70-200/2.8L IS but it's in the sickbay for now, and the 100-400 does well.
(I do landscapes but I'm not earning my living from that, though, so take this with a grain of salt).