If an engineer isn't doing well on their 80% project, a 20% project might be frowned upon, that is true.
Sure if you can get everything expected of you done in 32 hours, you can spend the remaining 8 on something else.
https://www.hrzone.com/lead/culture/why-did-google-abandon-2...:
> Why did Google abandon 20% time for innovation?
> In 2012 the firm began requiring engineers who wished to work on individual projects to run their proposals by their managers first. This was a significant change from the firm’s previous policy.
> In 2013 it was reported that managers had clamped down on staff taking ’20% time’ so as to avoid their teams falling behind in Google’s internal productivity rankings. Managers are judged on the productivity of their teams—Google has a highly developed internal analytics team that constantly measures all employees’ productivity—and so time spent on ’20% time’ projects would impact this.
2013 Google sounds like pretty much every other major company, in this area.