Continuing the hypothetical situation, let's say the company closes one major deal per month. The people who did not go on leave participated in 8 more deals. It's not discrimination, just being present should improve their future job prospects. Every deal means more contact with customers (who might later want to poach them), more likely they participated in some last-minute crunch time projects under the boss's eye, more unique circumstances/negotiations they had to navigate. Of course, if they are incompetent, more chance for that to be revealed as well.
I don't really disagree with your point, but personal experience tells me that inherent competence and motivation have far more impact on the value an employee can deliver than raw experience (on the timescales of weeks or months, which is the point we are focused on here).
How is "inherent competence" demonstrated? On that one deal when the boss needed the PowerPoint updated the night before a big presentation, Charlie was in the office and got it done. Nothing against Adam, but he happened to be on leave. Now the boss is deciding who to promote... it's just natural he's going to remember Charlie coming through and getting the job done when necessary. This is a simple example but multiply by lots of projects and lots of tasks and lots of meetings that Charlie participated in and Adam didn't, and the gap, in the boss's mind, likely widens.
Entirely agree, which is why I specified that all four are equal on those points in the premise. Once those are held equal, time, experience, reps, or whatever you want to call it, matters (or you have to find another explanation of how Charlie and Debby didn’t develop in work-related dimensions given the extra time, experience, and reps).
I've never met two people I'd describe as equally competent across the board, so it seems like an irrelevant exercise. We have also not touched on what personal growth and emotional maturity a person can gain in a few months away from work.
I suppose my conclusion is that as you argue, people probably will discriminate - but it is that part we should be pushing back against in order to make this proposal work, rather than just accepting it as an unavoidable consequence of parenting.
I want to also add that I have no children and no intent to have them; but I like the idea of the work culture we are describing here for other reasons. For example, acceptance that taking a sabbatical might be a significant positive step for some professionals if we can step back from the evaluation grind.
I took the max (paid) paternity leave for both my kids and am confident that my subsequent promotions were as they should be: against the standards for the next level without regard to whether or not I took any type of leave along the way.
The purpose of thought experiments is to examine some situations without bringing irrelevant factors in. We don’t need to literally know the same Adam and Charlie in order to reason about what matters and what should be disregarded in a given situation.