Leave if you're miserable. But stay with it after 2 or 3 years. Summary Good experience. Much work, but not much more than now. Learn to think, act independently.
Companies do fundamental research, but more now interested in the bottom line.
Government labs hire people. Maybe PhD shows people can retrain you to do almost anything. Academia much lower salaries, and companies can have interesting things to do. Physics faculty are learning to place students outside of academia. Not that bad.