I think people tend to paint things in a strong dichotomy always (black and white). So it is either super car focused or pedestrians only. And if you want to reduce cars therefore you must be the proponent of a pedestrians-only solution.
In reality there are much more nuanced solutions. E.g. if you have a small street with people living in it and the majority of the streets traffic comes from cars taking a shortcut between two main roads, maybe closing that direct connection and creating a dead end is the better solution that boosts the atractivity of the whole street, while at the same time making it more friendly to pedestrians, locals, cyclists etc. Cars can still enter. They just have no reason to do so, except if they live there.
The only downside is the loss of a shortcut, which might have impacted traffic on the main roads negatively.
In traffic there are often situations were all involved sides win if you take something away or encourage certain uses while discouraging others. On other paradox occasions, everybody can lose, if you add more lanes to a street.
In case of Mariahilfer it might be still possible to deliver, but the attractivity as a pure transit street got reduced, simply by showing what the priority is. If this impacts other transit routes also in a positive way, I don’t see why Vienna should do more of this thing — especially if it is willing to win the title of “City most worth living in” also in the future.