To pull an example of the opacity in how thing work - a lot of folks think of D&D Essentials as my baby, a project I created for reasons that range from the mostly correct (4e sales were in a freefall and the company was desperate) to the frankly hilarious (D&D 4e was massively successful, and I cooked up Essentials to sabotage it and manufacture my opportunity to create 5e).
Essentials was handed to me with all of the design direction set into place. The product specs - form factor stuff like soft cover, page count, the tokens in the various boxes, the fact that there were boxes - was all decided ahead of time. I was told that I was to take 4e and make something that was completely compatible with it but that could convince fans of earlier editions to give it a try. I was also told that this would be the new design direction for 4e because sales couldn't get worse, so why not? I think even the list of classes was handed to me based on market research or something, along with the mandate to not use the unified power progression.
(Amusingly enough, the unified power progression was a decision handed to the designers by management. Time is a flat circle.)
I'm also pretty sure I was the one stuck on stage to talk about it because no one else wanted to. It's not like it was fun to get in front of D&D fans in the time period.
Big picture, it's rare that designers on D&D set the direction for products. When I worked on the game, product pitches had to run an extensive gauntlet of folks. If the president of WotC said that we had to put five-eyed frogs from Mars in a product, that's what we did. When 5e was firing on all cylinders that process was pretty smooth. I have no idea what it looked like after I took a job working on Magic.
(As an aside Essentials sold well relative to the 4e line at that time. The folks who worked on the Essentials Starter Set, the one inspired by the Red Box, did a great job. That set sold a ton of copies, but it wasn't anywhere near enough to turn things around or at least slow down the endless parade of layoffs.)