AI detection in long-form content is a problem well-suited to training a classifier model. We have tons of verifiably-not-AI text from before 2022, and you can create tons of verifiably-AI text. As language drifts over the next few decades, it may get more difficult. But right now it is quite a manageable problem for languages with large pre-2022 text corpora available online.

The reason why AI detection tools other than Pangram are awful is because they are not really trying to solve the problem -- they just want to appear good enough to convince people to use them.