It's more like 6 once you include the HR screen and Department head meetings. 4 interviews seems totally unnecessary in itself. Especially if they were all 1 hour or more. Their current process would take 4-6 hours and that's only if they don't have any take home technical tests.

1) Quick phone chat 2) Technical interview - Either review or carry out technical test. 3) Team interview

Even then the team and technical interviews can be doubled up and the phone chat can easily be cut out entirely.