They're just different definitions of success.

For fusion the bar is "economically viable", in the current discussion for QC the bar is "cryptographically relevant".

They are comparable in that to meet either criteria, a variety of unsolved engineering challenges need to be overcome. For both, some of those problems have no clear and obvious solutions to which a simple application of resources and time will achieve.

Currently unknown innovations are required, unknown unknowns lurk in the dark corners, and all projections are relying on the assumption such innovations will arrive in a timely fashion and the unknown unknowns will be harmless glitches.

Neither are likely impossible, but betting on timelines is a fools game. This isn't the NYT publishing man-made flight is a million years away 2 months before the Wright brothers flew at Kitty Hawk, waiting for the right conglomeration of otherwise sound engineering to materialize in one place. It's like saying level 5 self-driving cars are two years away, a perpetually delayed technology for which all problems are well known and no new innovations are imminent.