This analysis is based on assumptions that don't really play out in real-life. For one, it assumes that those ten movies directed at different niches are hits within that niche 100% of the time, which just isn't the case in practice.
Netflix's content strategy in its early days actually resembled your Scenario B quite closely, but it ended up being super inefficient because you ended up with a whole bunch of $20m movies that were theoretically designed to be hits with different "taste clusters" (e.g. comedy, fantasy, horror, sci-fi fans, etc) but just like with any studio, a lot of them just didn't end up working. It also had a huge impact on quality; there's just no way a single division is going to oversee and ensure quality across 50, 60, 70 different movies a year.
Netflix's hit-rate with films is abysmally low compared to other studios, and part of that's a consequence of its quantity-focused "one film for every niche" approach.
Netflix films head Scott Stuber actually admitted defeat on that strategy a few years back, and the whole division's been restructured to focus on "fewer, better" movies. Essentially, they've restructured to be closer to a traditional studio, which makes fewer movies but spends more time on each. And if you're already doing that, why not just release them in theaters?