> Is the alternative not likely that they would have spent a decade fighting a losing battle over office software with Google and Microsoft? Paper was a great product but the big guys have vertical integration so companies prefer their end-to-end solutions (GSuite etc) and I don't see how Dropbox could have easily overcome that.

Slack, Zoom, and Notion all argue against that. Yes, they have to compete against Google and Microsoft's integrated solutions, but they're good enough that they have held their own. Of course they would be bigger if Google and Microsoft didn't have such products.