This is very much true. We do take-home interview questions where they bring the output to the interview and we talk through their solution in person. We'll ask how long they took as a way to normalize expectations and also adjust the interview question to take more/less time in future instances.

This does two things. In the long run, the time required converges towards where we want it to be (ASSUMING honest answers), and by bringing you in to talk through things, we can easily tell if these thoughts were your own by challenging you on specific parts of the prompt.

This is less than ideal since it costs the interviewee time, and time isn't cheap, but we've found that advance prep removes an even bigger wildcard in interviews: how you respond to interview stress.