Google is an incredibly complicated situation. Yes, it's impact-driven. But many other variables affect how your impact is perceived. For amusing reasons, over the past decade, the number of people who can and want to work on the core parts of google3- the load balancer/front end/web server/search/ads- has been dropping. No CS grad wants to work on a 15 year old web server that is mostly patches to deal with odd cases and a million tests that fail if you look at a load bearing comment oddly. The dwindling pool of experts has seized the memes of production (ha) and has the ability to work less because they are absolutely needed.
The best anecdote I ever heard from an SRE was "the VP was chagrined when I told them it didn't matter I was in a nerf war, because nothing was broken or needed to be fixed, but they still saw my point and let me continue" (I used to work in an SRE area that overlapped with an SVP's preferred meeting room so Susan Wojcicki was always getting pinged by a rogue nerf bullet).
As for slackers? Sure, when I joined around 2008 there were definitely folks who were slacking off. in fact they got rid of sabbatical because so many people were taking it then coming back and quitting.