Zoom/telephoto lenses being 'not sharp enough' is one of those things that *used* to be true (we're both old enough to remember that), but with teles since 1990 or so that's no longer true. Even the Nikon/Nikkor 'D' series film-era teles were fine for fine-grained film, and now in the digital era they're fine on a 24MP (a bit better than film) body. If you go way over 24 (e.g. Nikon D850) and 'pixel-peep' you can see some softness, but for printing under 40" on the long side, that's invisible. Who prints bigger than that? Maybe Mangelson...? (a name my spell check keeps changing to 'Angels on' - what the...?)
Now there's the choice beween constant aperture and variable. Constant is great for wildlife photographers as you have a fast aperture at the long end of the tele. But they're bigger, much heavier, and much, much more expensive than the VA. I'm a landscape guy, looking for long-in-focus, so I don't care about fast at the long end - and variable aperture is great for me. About all I miss out on is the weather sealing that those CA lenses often have - and I have a heavier wallet to drag around. :-)