"I guess it depends on what employees are looking for in their career - to be the best they can be, or live a laid back lifestyle."
You're not being the best when you burn out. You're killing yourself and your productivity with it. We have decades of research concluding that productivity falls when you're overworked.
"The company (in this case, Amazon) got great results from its employee, the employee had a good experience"
The employee does not have a good experience when they're working themselves to exhaustion.
"If an employee puts in a solid 2-3 years and delivers great results for a company, "burns out", and then moves on to a new role or company, is that really that bad?"
Yes, because companies shouldn't have to work their employees to the bone to extract value from them. A long time ago, we decided that it's cruel, and created labor laws. Where have you been?