These ideas all seem like bandaids to me if they aren't personal goals that you care about. I've seen studies that show that burnout is caused by sustained imbalance between your personal goals and how you're living your life. This can also happen retro actively. For example, if you were to find out that you weren't going to get paid for a job you'd been working the last 6 months on, you would almost instantly be burned out. That is, if you were doing it for the money of course. Your personal goal is to spend a certain percentage of your time on things that will increase your wealth, and if you weren't to get paid, the sudden overwhelming sense of losing six months would burn you out immediately.
Likewise in a startup, I think the studies would say that you find yourself burned out because at some point, something inside you says, "80 hours a week for the last year wasn't really completely in line with all my personal goals. I have a goal to have personal relationships, spend time with my family, and exercise, yet this startup is the only thing I've been doing." At some point a voice inside says, "It wasn't worth it."
People have very different goals, so results will vary as to what causes burnout, but as a boss, something I know will cause burnout is anything that will pull the rug out from under an employee regarding benefits that they expected to receive. For startups this is super tricky because some employees are expecting an IPO with big payouts, and when they get disillusioned about that, there's really no way to stop the burnout.