No not a perfect system, but generally works well.
My main objection is that it's easy to get in the thinking that it's "your" slot and being upset when a more junior pilot gets promoted, something I don't think was the original idea!
If someone is really good they should be able to accelerate their career (in my opinion) without getting viewed as a brown noser by other pilots.
Please note that in the scenario I gave it wasn't the company management who said "let's take this guy!"