The legal question is a distraction. GPL was always enforced by economics: reimplementation had to cost more than compliance. At $1,100 for 94% API coverage, it doesn't. Copyleft was built for a world where clean-room rewrites were painful but they aren't anymore.
I don't think it's been established that clean-room rewrites are no longer painful. We don't know if chardet could have been rewritten so easily if the original code wasn't in the training set.