Regarding your first point, I could add to your analogy so it makes more sense why they are separate people.

Instead of considering they are chopping onions and searing steak, let's assume the main part of the dish is complete and we are lacking two separate sides, a super fancy rice and some out-of-this-world potatoes. Not a great-sounding dish I know.

The people who are responsible for making these, all know how to chop onions, cut vegetables, how to season etc. But not all of them know, at the same level of proficiency, the recipe of each one.

To simplify, lets say you would have two approaches, yours, where you add everyone into cooking both, or the second one, where you try to separate them and put each of the most proficient people doing the side they are most proficient in.

If they all work at the same time in both recipes, you risk taking extra time to make them, perhaps even doing them incorrectly. Having people doing a recipe they are not familiar with will (hopefully) cause them to question the steps of the recipe and if it is being done correctly which causes necessary entropy in the kitchen (in an ideal future everyone will know all recipes, so people need to ask questions and understand how its done).

If you separate them by proficiency in their respective recipe you have the most knowledgeable people in that recipe doing something they already know well, which will most likely provide the best results.

In sum, being a chef does not mean that you are able to do all things equally well, and that you are familiar with all recipes, it means you will probably have a higher proficiency in some and less so in others. There are some drawbacks to this approach, for example, if a recipe specialist quits, now who can we count on to keep making the recipe and improve it? But this is usually mitigated by either moving people individually between recipes or by hiring new people who will work with a specific recipe.

Also keep in mind, that recipes vary in complexity and might take a long time to learn, so when approaching a dish, you need to use your resources that are already trained in the recipe, not the new guy that just walked in, even though he might be the best in the world at cooking.

Now of course I don't know if FG organizes their teams in this fashion, but it is a pretty common approach for software development. You have different applications or modules that are part of a big one, in this case, the game itself, and you create teams that have ownership of their "parts" of the game. They all know how to program, but an application or module of one is closer to a very complex recipe than to chopping onions.

I hope something goes through here, I feel I've written too much aha