All interesting deadline-based work involves some degree of overworking at one point - not just startups, but journalists, project managers & many others. But the problem with asking 'successful bootstrappers' whether it was all worth it in hindsight is survivorship bias. They survived & got successful. Ask someone whose great idea failed because they fell ill & you get a different picture - especially in the US where leaving a job to startup can mean foregoing medical coverage.

There are times when a burst of excessive work is both necessary & beneficial - but it's not universal.