The E12 looks like a proper highway that in many places would be at least 90km/hr (possibly a variable speed limit depending on the amount of traffic).

Here's another local example, Granville Street, which is also 3 lanes but definitely denser/busier: https://maps.app.goo.gl/4X6RRVKUFKNoFA248

What tends to happen in practice is that people here drive faster than the speed limit on some of these, e.g. both my examples I would say 70km/hr is a lot more common than the actual 50km/hr speed. On smaller streets, lessay: https://maps.app.goo.gl/5AaW7FgiuK5ti6sy6 you would typically go slower than the limit, especially if there are more cars parked, or pedestrians present or more traffic. In some of the smaller streets traffic can't even pass both ways when there are cars parked and people alternate the right of way.

I tend to think of speed limits as a way to fine drivers rather than a true safety thing. If you want people to drive slower you need to create the conditions that will make them drive slower. In many small streets that tends to be speed bumps (which I don't like) but there are other solutions. You want the speed to feel natural to the drivers, i.e. that most reasonable people would drive that speed in order to be able to respond to what they predict might happen.

Reducing speed limits feels like a cop out. A better solution includes better thinking about city design, roads, and transit. Reducing the speed limit is unlikely (at least around these parts) to actually result in people driving slower.