You say that speed limits shouldnt be enforced as they would be a “symptom” of poor road design. This abolishes the speeding drivers from their own responsibility for violating the traffic rules.
You misinterpret the design choices shown in the video as the opposite of “bad road design”, therefore “good road design”, which implies a generality. However these design choices are made solely and explicitly to enforce speed limits. They have disadvantages in other ways e.g. if you make spots where only one car can pass at a time, it makes traffic less efficient. These disadvantages wouldn’t be needed if people would uphold the traffic rules by themselves.
Good design or bad design, many people will speed if they can get away with it. With a proper enforcement through speed cameras, and proper penalties for speeding, e.g. losing your licences for repeated offenses or having your vehicle impounded, could equally serve for enforcement. They are just more expensive, so making design choices is prefered by some countries.
But still people who speed chose to speed. They chose to violate the traffic rules and they chose to endanger other people and themselves. So speeding is never a “symptom” of road design. It is always a “symptom” of selfish assholes that should not be given the right to operate dangerous vehicles.