But are we hitting that power density ceiling yet? It doesn't seem so, we're not even in the "big enough to have ignited" range, only scraping at the door of "big enough for scientific break-even", but have already blown any reasonable chance for such designs to be cost effective even if they were to be mass produced.

Massive superconducting magnets generating megatons of force, building-sized vacuum chambers that are almost guaranteed to leak some amount tritium, which only adds to the unavoidable regulatory burden imposed by the fast neutron environment, activated structure and every day production of weapon-grade material etc. etc., even if the current technology magically works tomorrow, it's still an economic dead-end.

The present fusion crop is megascience at its worst, draining public funds for something that can't possibly ever work and producing very little substantial science in the way. We need to take a step back and reassess. At least Helion is trying a new path, even if they are likely to end up in a similar dead-end.