Am old enough that this was status quo for part of my career, and have also been in some groups that did this as a rejection of modern code review techniques.

There are pros & cons to both sides. As you point out it's quite expensive in terms of time to do the in person style. Getting several people together is a big hassle. I've found that the code reviews themselves, and what people get out of them, are wildly different though. In person code reviews have been much more holistic in my experience, sometimes bordering on bigger picture planning. And much better as a learning tool for other people involved. Whereas the diff style online code review tends to be more focused on the immediate concerns.

There's not a right or wrong answer between those tradeoffs, but people need to realize they're not the same thing.