Please be aware though, that there's always going to be a large population segment that will desire to proceed directly from point A to B in comfort.
Unless by "public transport" you're including "government owned autonomous taxis", public transport will never be attractive to that population segment.
How large do you consider this population segment to be?
People generally prefer to a) be comfortable, and b) proceed directly from point A to B with no interstitial bullshit.
You almost never get b) with public transit as commonly realized today.
Just. Build. A. Train.
But if someone wants to go directly from point A to B in a "gimmick jet", why should we try to prevent that?
I'll reiterate with your example. Building high-speed trains, and developing "gimmick jets" are not mutually exclusive endeavors. It's clear that you are not personally interested in a "gimmick jet", but there are people who would be. Why exactly should we be stopping those people?
I do think that there are big challenges in people transport (mainly around cars and planes) and this does not solve any of those challenges, as it does not scale. So I see it as a gimmick: cool tech to show off.
I'm all for letting everyone with an idea try it. But we need to apply our safety etc. standards consistently. A lot of these new transport startups are really just regulatory arbitrage where they're relying on not being regulated because they don't fit existing categories. Make it legal to build high-speed trains with the same (low) safety, noise pollution, interoperability etc. standards as gimmick jets, and we'd see a lot more practical transport getting built.