As I wrote someplace else before: his job was done by dogs and monkeys before, so it's hardly mission critical for him to even be conscious. In fact, the mission would have been considered a great success even if he had been unconscious the whole flight, as long as he survived. His presence was the key point.
Throughout Mercury, the astronauts had to fight for control elements to even be included in the spacecraft because automation was considered the safer option.
Don't get me wrong, I'm a big fan and these steps were incredible milestones, and I certainly wouldn't have wanted to switch seats with anyone.
Here, I am sure Bezos can/would argue that "someone had to make observations on the performance of the rocket and the spacecraft, as well as himself throughout the mission". Sure, the goal here is commercial, but it's hard to argue that Gagarin's flight was made to gain pure scientific knowledge to finally answer the pressing question of how humans react to spaceflight, rather than political/technological.