Every PhD program I'm aware of has a final hurdle known as the defence. You have to present your thesis while standing in front of a committee, and often the local community and public. They will asks questions and too many "I don't know" or false answers would make you fail. So, there is already a system in place that should stop Bob from graduating if he indeed learned much less than Alice. A similar argument can be made for conference publications. If Bob publishes his first year project at a conference but doesn't actually understand "his own work" it will show.

The difficulty of passing the defence vary's wildly between Universities, departments and committees. Some are very serious affairs with a decent chance of failure while others are more of a show event for friends and family. Mine was more of the latter, but I doubt I would have passed that day if I had spend the previous years prompting instead of doing the grunt work.

In the future the llms can answer those questions for you by listening and feeding you answers into your headset.

The process you describe is a gate keeping exercise which will change to include llm judges at somepoint.