Power BI cannot display more than 1000 unique values, although useful in some models, it does not correspond to the exact storage or engine behavior being evaluated.

High cardinality increases memory usage and slows down visual rendering

A tuning technique that targets refresh time rather than the interactive query latency discussed in the prompt

There is no impact from high cardinality, although useful in some models, it does not correspond to the exact storage or engine behavior being evaluated.

High cardinality columns cannot be filtered, however, this points to a general optimization idea and not the concrete query execution mechanism tested in the question.