It absolutely is reasonable to expect people to drive below the limit. Speed limits are just that, maximum upper bounds of how fast you legally can go, not "recommended" speeds or minimum speeds, nor are they necessarily "safe" speeds. It's just a legal upper bounds.

It is a drivers responsibility to drive for the conditions. If conditions are calling for driving 40% slower, then that's what you do and suck it up.

If too many roads have conditions that require that, take that up with your municipality to fix the situation. Or, even better, advocate for better public transit and trains, and designing cities to move people, not move cars.

Driving for the conditions mostly means weather.

If there's cars parked on the side constantly, and that's supposed to slow you down significantly, it should be baked into the speed limit.

From what I'm aware of, you're not actually expected to slow down drastically from parked cars.