for one, assuming it takes 5 yrs after graduation for an average engineer to reach senior at a tier-1 company (esp. Google) is simply untrue in today's environment. Besides the point that promotion is highly dependent on manager, team, org and timing (think about reorgs and project cancellation/deprioritizations), the average timeline for promotion nowadays takes longer than a few years ago.
You're just wrong, at least w.r.t. Google. Folks who are good and destined for senior in 4 years do not wait for a good manager/team/project - they seek them out and take their career into their own hands.
didn't I put "average" in the comment already? (and to be fair, this is the group the post was talking about when making the calculation). I know and have helped some brilliant engs at google reach l5 with much shorter time frame, but it's not the norm.
given you seem to be from google, there are various stats w.r.t promotion timeline that offers more insights about the average case internally
