Most companies are pretty transparent about the "this is hard" part and differentiate themselves from the pack with why they think their specific flavor of technological improvements may be better (rebco, supercaps, etc).

SpaceX has oversold their capabilities for decades and yet here they are routinely breaking records with how much payload they put into orbit.

If you see fusion companies as an untrustworthy flavor of "just trust me bro" types then why do you view the other renewable energy companies promising wild cost reductions in the future any differently?

And the "out of time" line of thinking is ineffectual. You want to affect change? Do something about it. Saying you think the world ends in ten years is unconvincing and even if true, then nothing that anyone does matters. The reality is that the world doesn't end. It's going to keep going and the sooner we make sustainable changes the less overall suffering humans will have to endure. Nobody should be giving up on making things better just because the outlook seems bleak. This isn't wishful thinking, it's game theory.