>Secondly, the author believes that senior developers, who likely have 10+ years under their belt if they're senior, need to spend a solid month revising in order to be successful landing a role there.

FWIW, I joined FB at 20 YOE and spent about 3 hours on Leetcode problems just to get my mind back to being able to handle "stupid computer" tricks. Array manipulation, algorithm cleverness, etc. are things that I hadn't really done since the early days of my career. Aside from that, the only real challenge was a system design interview with a VERY junior engineer where I had a really hard time keeping things at a level they'd understand while not coming across as patronizing.