That's not how it works. The wider the aperture, the worse the aberrations. IF you can make a lens usable at f/1.8, it will be tack-sharp stepped down. That's why wide primes have a reputation for being super-sharp.
Roughly the same optical design, limited to f/2.8, will be better in all respects.
A good way to think about this -- oversimplified obviously -- is you have a bunch of functions you're trying to cancel with e.g. a linear combination. If you look really close to the center, it's already a flat line. If you step out a little, two are adequate (have the slopes cancel). As you go further and further out, things become increasingly wonky. That's why you have super-complex designs for an f/1.8 zoom -- to get that cancellation right -- but even a single element works fine at f/22.
There actually were f/1.8 zooms all along, but for applications which didn't demand that sharpness (TV and CCTV). You can pick those up cheap and see what happens. They're sometimes fun on a real camera too (many will span a μ4/3 sensor with just a tad of vignetting).
