I can't remember which generation exactly had this shift, but yeah around the iPhone 12 they went really heavy on the processing, so instead of a noisy but sharp image you got a smudgy mess. Later generations improved on that but you still see this when zooming in or in low light.

The processing pipeline also started imposing its own opinions on your photos, adjusting the brightness of dark areas and bright areas to even things out, increasing saturation, etc. This has generally trended towards more processing over the years.

In a picture from a standalone camera (or an old phone back when the processing pipeline was basically just debayering, white balance, chroma denoise, and a gamma curve), you'll actually have contrast between shadows and highlights, which, when done well, looks great. When done poorly, it looks terrible (blown highlights, noisy shadows), which is the whole point of the processing pipeline -- on average (random user, random scene), you're better off reducing the overall contrast in the image with local adjustments, even if that turns some excellent photos into boring ones, because it'll turn a lot more bad photos into acceptable ones.