I’m not quite sure what the analogy you’re considering is, but if we’re equating fusion power plants to transistor-based circuits, I think we’re currently proving different types of solid state diodes are possible to create in a lab.

I suppose you could make a timeline of technology development, fusion is still in the lab stage but past the conceptual and experimental stages and into the early making it practical stage with several approaches competing for first to actually achieve something useful.

What’s left isn’t just straightforward work, but a lot of finding and fixing inefficiencies and that sort of work.

No, because transistors were clearly going to be useful.

Fusion (especially DT fusion) has a good chance of never being useful (except for H-bombs).

These comparisons with old embryonic technologies also miss the point that lots of embryonic technologies never go on to success. Focusing on the rare ones that did is survivor bias.