That's why the speed limit is 25 (lower when children are present in some areas) and not 35 or 40 etc. It's not reasonable to expect people to drive at 40% of the posted speed limit the entire way. We're also not talking about zero visibility (e.g. heavy fog). We're talking about blind spots behind parked cars, which in dense areas of a city is a large part of the city. If we think as a society in those situations the safe speed is 10 mph, then the speed limit should be 10mph.
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.
Maybe not, but if parking is so dense as to cause safety issues, and cause conditions to require slower driving, the city should still be addressing it.
I know, it's not reality in most cases, but it goes to show how poor our infrastructure is and underinvested in.
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.