You're placing too much emphasis on completing things. The vast majority of startups won't be around for the length of time you're suggesting. The vast majority of BigCos have plenty of people who can finish projects and maintain the status quo.
Both kinds of companies need people who can start major projects and get results quickly.
"You're placing too much emphasis on completing things."
Probably, I try not to hire folks who can't complete things. I think you're off on your startup timing through. I know lots of startups that took a year to get to their MVP and then another to get to something they were willing to call 1.0. But by the same token I don't think of things you could do in a weekend and ship as being 'startups'.
Both kinds of companies need people who can start major projects and get results quickly.