We have small quantum computers, we don't have big ones.

We have fusion power on small scale, we don't have it on commercial scale.

Seems to be the same argument.

We have small, usable quantum computers and have grown them for years.

We have never had fusion power on a small scale (we have had fusion ignition/reaction, but never [afaik] generated usable power), let alone showed continuous growth in scale of that power over the years.

They're not the same. Fusion is a 'science' problem, quantum is (mostly) an 'engineering' problem.

Re-read my comment and then point out the spot where I advocated ceasing research and development of anything.