This is true in one sense; in another, we can see a huge sustained fusion reaction hovering above our heads all day to prove it is possible.

This is a bit more than a quibble. Before fission was demonstrated, the idea of either a fission explosion or a self-sustaining reactor was entirely theoretical.

I've been following fusion research for many decades now, and I'm still very hopeful. Yes, it's gone a lot slower than expected, but funding got slashed and slashed again. There's no reason to suppose we can't do it, and it seems likely that we can.

However, I would still not use the world "will" as you do in your headline. Many things might yet go wrong. Fusion might simply be too hard for us for some unknown reason (I think this unlikely but I can't rule it out). Society might collapse. Fusion might become practical - but through a different path not connected to JET.