Cool, so we should totally be able to factor 21 (or larger numbers)…. When?

You brought up gate noise, there has been quite a bit of progress on that problem.

> so we should totally be able to factor 21 (or larger numbers)…. When?

Just because we solve one problem doesn't imply all the problems in QC are also instantly solved. I guess it does if you assume noise is the only problem and once is it solved the engineering is trivial. That is not the case. Even assuming all foundational problems have been solved, figuring out how actually engineer and also mass produce large numbers of gates, will take a while.

As the article pointed out, going from 15 to 21 requires a 100x increase in gates.

As the article that you posted under says:

"Because of the large cost of quantum factoring numbers (that aren’t 15), factoring isn’t yet a good benchmark for tracking the progress of quantum computers. If you want to stay abreast of progress in quantum computing, you should be paying attention to the arrival quantum error correction (such as surface codes getting more reliable as their size is increased) and to architectures solving core scaling challenges (such as lost neutral atoms being continuously replaced)."