[Sirened]

Yep... If you're going to go through the effort of completely rewriting a piece of code to try and dodge an AST analysis algorithm, you've effectively just done 70% of the work and put your grade/position at the institution on the line. It's not worth it, and so people don't tend to do that. It's the same thing with plagiarism—students could very well resynthesize a stolen work in their own words. It would still be plagiarism, sure, but it's also putting in a large amount of effort while still being risky.

[Aeolun]

If you rewrite everything you steal (e.g. never copy/paste), it’s no different from using an especially well written source.

[Sirened]

Well, no. It's still plagiarized if you fail to communicate that it isn't your original work. You can't just steal ideas from someone else's paper, even if you rewrite everything. If you rely on another paper for inspiration, you have to cite it. If a student submitted a paper that was just another paper entirely rephrased, that would not be acceptable in the least even if they cited their source because the expectation of writing a paper is that you contribute something novel and not just regurgitate someone else's argument