My friends at Amazon are killing themselves.
The ones at Google, well... I'm impressed by how little they can do.
I guess it's also heavily management dependant. If some middle manager doesn't give a crap and somehow can get away with it those below can slack as much.
If the cause of burnout is disillusionment - aka, you are such a small cog and your work doesn't seem to matter, despite how hard you actually worked - then moving to a different, but still big company, will not change that. Startups, imho, is where to move to, in order to feel impacts.
If the cause of burnout is project-based - aka, you just don't enjoy or feel the project is worthwhile - switching companies might work (a different project).
There's many other causes of burnout, and each will require individual solutions - there's no one size fits all.
either you're doing too much work, or everybody else is doing too little. Cut back.
As for promotions, if you intend to do 4 days, prepare to face zero career progression in the same company - unless you're extraordinary and indispensable. But this is the price you pay for a 4 day at this point.
The top companies are political nightmares because the pressure and competition levels make them insane.