> Blocking exits does not in any way improve the road itself.
Incorrect. It improves the conditions of the road for local drivers, as well cyclists and pedestrians. Which is exactly why Portland did it. Unless you have an alternative explanation?
> The fact that through traffic is technically possible does not mean it is 'prioritized'.
It shows that they've prioritized enabling through traffic over other concerns.
It's not all that different from road diets. Road diets usually reduce the carrying capacity of the road, making it "objectively worse", in your parlance, in the service of other goals. Diverters accomplish a similar function.
Blocking exits only fixes things through second order effects. The direct effect is negative. If we could stop through traffic via other means, we wouldn't want to block exits, but we would still want bike lanes and speed limits and road diets in residential areas.
Blocking exits does not in any way improve the road itself.
It just inconveniences people that are improperly cutting through more than normal drivers.
The fact that through traffic is technically possible does not mean it is 'prioritized'.