Virtually nothing, except weight, was sacrificed to make the 18-35mm f/1.8 zoom. That's why it's impressive.
It's possible due to things like:
- Much better lens coatings (allowing for more elements without flare)
- Computer modelling
- Being able to better machine aspherical elements
On integrated cameras, like an RX100, we can do even better due to digital. We don't need low-distortion, but just well-characterized distortion which a computer can invert.
Those old lenses -- at least the ones still working -- do have build quality. Adjust their prices at the time for inflation, and have a look at modern Zeiss, Leica, and other premium lenses. You'll see similar build quality.
For fun, next time you're looking at old lenses, pick up a Quantaray too, for fun. Or most older (before around 2000) Sigma lenses. Or other off-brands. You'll see unparalleled build quality, but in the other direction -- eighties-era plastic. The optical quality is bad. Not "fun" bad, "vintage" bad, or "whimsical" bad, but just bad.
When we look at older stuff, we tend to look at stuff which stuck around, but even that Quantaray is high-end compared to an older consumer camera. Most people who owned a camera had a non-SLR one. You looked through a little window on top, and the pictures were shot through the main lens. Those were even worse. Or a disposable (a single plastic element lens).
