The focus on f-stops was/is for the same reason people chased high ISO film in the old days, and "ISO" on sensors now, and the focus on extremely long tele's al

The focus on f-stops was/is for the same reason people chased high ISO film in the old days, and "ISO" on sensors now, and the focus on extremely long tele's also. This isn't about getting the best image possible but about capturing something you otherwise couldn't get at all. All of this gear is about flexibility to handle poor lighting conditions, things moving quickly, etc. If you are product photographer with a room full of lighting equipment you are going to pick the right lens for the job and make the room work. Other people rarely have this freedom. It's worth noting that in the last couple of generations of digital sensors, we're objectively in a better situation than fast film was, so that loosens the need for fast glass a bit. The same is true for widely deployed mostly ok physical image stabilization systems.