Maybe they are at the average job level but just aren't feeling challenged? They did get a promotion, so they can't be that bad... Maybe they're just bored? Either way, leaving a secure, good paying job is almost always bad advice, especially without a firm plan in place..
While L4 is terminal at Google, it's still not particularly high achieving for 6 years of career. Google also doesn't make it easy to jump from L4 to L5 either, so OP may feel like they're stuck in a rut because of that as well.
100% in agreement. One major risk you’ve accumulated by slacking is that you may not easily get another job if google does eventually push you out. Your next employer will say, tell us what you’ve done - specifically. At some point you either have pride and integrity as a person or you’re an asshole. Google might tolerate that now when you’re young but I think fewer and fewer others will as you age. It sounds like you have some time to make some changes in your life - I would recommend you start there before kids and other life events take priority.
