Eric Berger wonders if it was a mistake.

As he notes, it was just overtaken by events.

But this is a fundamental flaw in how NASA does planetary missions:

And yet the Falcon Heavy has not spurred the development of a rash of new science missions. NASA simply has not set up the science community to take advantage of a low-cost, heavy lift rocket, said Casey Dreier, space policy director for The Planetary Society. “The incentive is just not there for scientists,” he said.

Primarily, mission planners and scientists are concerned about keeping the cost of the spacecraft down, and controlling its mass. The decision on a launch vehicle is typically left to NASA and its Launch Services Program. The Falcon Heavy really has not been around long enough to shift that calculus. Dreier said there is a chance that the larger Starship vehicle—which will dramatically change mass and volume constraints for science missions—could eventually change how NASA selects science missions.

I think that in general they would be much better off if the program manager was simply allowed to choose their own launch system as part of the program within their budget, rather than having to work within the constraints of the one chosen for them by NASA. And of course, it would have paid off much sooner in the case of Europa, because no sane program manager would have chosen SLS for it, if they had to pay for it.