Brightline is very successful, part of which is due to having so few stops, something that a public railroad could never get away with politically. The Amtrak trains stop so often that they spend very little time at their top speed.
They had 1.2 million rides in 2022, that's good by any measurement. Pacific Surfliner in Southern California is a wildly successful intercity rail and only had 1.6m rides in 2022.
Some people may use them to commute but it's not primarily commuter rail, would be my guess.
The San Diego trolley has 63 miles of track and 34 million riders in 2022; but that's an entirely different type of rail that serves a different purpose. Even if it eventually reached all the way to Los Angeles there would still be uses for commuter and intercity rail.
Many places in Europe have the various types of rail all sharing the same "lines" or stations, but the ICE is a completely different beast than the Regionalbahn or Regional-Express.
With that said, as you point out, it's a new intercity service that is actually operational, popular, and being used today, which for the US is an enormously rare feat.