It's actually much more true the other way around: if physics is somehow fundamentally preventing you from fusion ignition, then focusing on engineering or economic issues is a complete waste in money and a dead end. Because while economics and engineering change over time, physics[1] does not. It's like spending money trying to solve the economics challenges of a perpetual motion machine[2].

[1](Although our understanding of physics does.)

[2](...which fusion is not)

A showstopper is a showstopper. Yes, physics can rule things out. But so can economics. There is no reason to give the first priority over the second, if the second is sufficiently bad. And I will claim those practical considerations render fusion very dubious. And yes, they change over time: they have gotten WORSE for fusion. It used to be that fusion was competing with fission to be that post-fossil energy source. That was, perhaps, not too unreasonable, especially if the fission had to be with breeding. But now, it competes with dramatically cheaper renewables.

Yes there is because again, physics does not change. Physics showstopper rules out all others.

To the end user, it doesn't matter if physics or economics caused a technology to be useless. It's still useless. And it doesn't matter to the financier either. In either case, any investment he made is lost.

Your attitude is a reflection of a culture that considers physics to somehow be a deeper subject than engineering, facing more fundamental and important problems. The details are "just engineering", somehow not important or relevant.