You'll be well into diffraction by F8 on a crop sensor though so if you rarely shoot wider you'll be missing out on that sweet spot.
That's not my experience. I've been shooting a variety of crop sensor camera bodies since 2006, with an increasingly large collection of lenses. I'm an experienced pixel-peeping detail resolution hound. I've tested most of my lenses through their range of apertures to find out where diffraction softening starts. It varies quite a bit from lens to lens. My best lenses are sharpest at around f4, in other words diffraction softening starts just past f4, whereas my poorest lenses are sharpest at f11.
To expand on and explain that a bit of diffraction softening theory is appropriate.
Diffraction image softening is something that happens at all apertures. My semi-educated understanding (to which I welcome corrections) is that diffraction image softening is caused by the diffraction (bending) of the light rays as they pass close to the edges of the aperture. Those bent rays are thus unable to participate in the sharp focusing of image detail, and instead scatter elsewhere to soften the image and lower contrast. Real lenses however have some imperfections which are reduced by stopping the lens down, reducing the aperture.
Since the image is formed by the total amount of light entering the lens, i.e. the diameter of the effective aperture, which is a circle, the amount of light producing the sharply focused image is proportional to the square of the diameter of the effective aperture. The size of the diffractive edge of the aperture, however, is simply proportional to the diameter. So the larger the aperture the less is the proportion of diffractive edge to image forming area, the smaller the aperture the more diffraction. It's a more subtle and complex example of a square law effect than in local artificial lighting power calculations.
So if lenses were optically totally perfect image forming devices, the larger the aperture the less diffraction image softening. They'd be sharpest with maximum contrast wide open. Perfect lenses are however a practical impossibility. The closer lens makers get to perfection the much more expensive the lens becomes to make. For economic reasons most lenses suffer from a number of optical image-forming imperfections, such as spherical aberration, which get smaller as the lens is stopped down. Diffraction image softening increases as the lens is stopped down, but so long as the stopped down
increase of diffractive softening is less than the
decrease of image softening due to optical imperfections then the lens will sharpen up as it's stopped down. So each lens will have its own individual optimum aperture where the sum of the softening due to optical imperfections and to diffraction will be at a minimum.
In fact since most lenses have better central sharpness than edge sharpness, and the effects of aperture-related optical imperfections often hit the image edges worst, the best aperture for central sharpness is often wider than the best aperture for edge sharpness. The best aperture for overall edge to edge sharpness will therefore be a compromise between the two.
Going back to my own lenses on my crop sensor camera I do not find, as you suggest should be the case, that I'm well into diffraction softening by f8. That's only true of my very best lenses. Most of my lenses are sharpest around f5.6 to f8, and what the sharpest aperture is depends on whether I'm going purely for central subject sharpness, or edge to edge overall sharpness.
Most of my photographs aren't taken with any of my optically good lenses, however. I usually take a camera with me whenever I go out, just in case. Often I never take it out of the bag, but I get so annoyed if I leave it at home and a good photo opportunity turns up. Not knowing in advance what kind of photo opportunities might turn up I usually just take the camera out with only one lens, a general purpose Swiss Army Knife of a lens whose primary virtue is a very large zoom range. In pursuit of the large zoom range some other aspects of lens image quality have been sacrificed. With that lens if I'm going for best edge to edge sharpness with that lens I'll often stop it down to f11.