I think we actually agree -- I've stated that I think it should be a differentiator, not a requirement. As in, if you have people with two similar levels of skill, then yes, it should push one person over. If you have one person with less skill, but who mentors more, I don't think that person should leapfrog someone with more skill but who mentors less (relative to the first person).
Let me more succintly state some issues I have with this:
- Who benefits? You moralized this as being "selfish", but as an employee of a company, you are selling your labor (and more importantly your time) to a company for a wage. It is in your best interest to carefully examine EVERY bit of value you hand over for the wage you receive. No one else in the transaction is going to do that for you -- benefit to the company and benefit to coworkers is great, but you need to judge that against the wage you're receiving.
- Where is the pay commensurate to the increase in efficiency/intelligence in the company? I don't see it in the charts on the original link, the difference is too marginal, for the benfit you're providing the company. If that's the case, senior engineers are just being taken advantage of.
Again, I'm not denying that there are more senior people who trained and mentored me. There absolutely have been, I've had some of the best managers, mentors, and coworkers anyone could ask for. I don't think the fact that they mentored me should influence whether they get their next promotion -- sure it might be good color commentary, or a differentiator if there's a tie when the decision is being made, but it shouldn't be on the rubric. This is how average engineers get to be "senior" whatevers and "architects" -- by putting in time and playing the rubric instead of bettering their skills.