That’s what’s usually gets said about lots of alternative fusion energy generation methods that later turn out to be impossible to have net-positive energy generation.
And this is just one example. Another example: tons of medical compounds end up dropper at the medical testing stage because of their nasty side effects or it turns out their “positive” effects are indistinguisheable from the placebo effect.
The point being that you can’t actually extrapolative from “neat concept that shows potential” even to merelly “will works”, much less to “will be a great success”.
PS: Equally, one can’t just say it’s not going to be a great success - being a “neat concept that shows potential” has a pretty low informational content when it comes to predicting the future, worse so when there are people monetarilly heavilly invested into it who have a strong interest in making it look like a “neat concept that shows potential” whilst hiding any early stage problem.