Making interviews efficient and making them easy are orthogonal. It depends on what attributes your organization is trying to select for.

To select for people who are willing to commit to a slow bureaucratic organization, make them go through repetitive interview rounds spread over many weeks.

To select for people who do well under pressure, make the interview stressful.

To select for people who can solve challenging problems, make the interview challenging.

There's no right answer as long as your hiring process is tailored to select for the attributes your company needs.