The need for f/1.0 and even f/1.2 lenses was mainly due to sensitivity limitations of film and early digital sensors. With modern digital sensors, we can get image quality at crazy high ISOs like 6400 or even 12800 that we only dreamed of at ISO 1600 only a decade ago.
Those 'legendary' 50mm f/1 lenses were legendary for one thing: f/1.0. Otherwise they were significantly compromised compared to slower lenses in exchange for that fast aperture.
Shooting fast apertures isn’t to keep the iso low.
And although the 200 f2.0 and 200 f1.8 have “almost” the same aperture the small difference in pop is pretty awesome. I would’ve liked a 50 f1.0 L II instead of the RF50, I could then stop down to 1.2 and not have insane vingnetting ...
Couple weeks ago stumbling around Seoul, one second hand shop had 50 F1.0 on shelf, with sticker that looked like 430k Won (= ~$400). Naturally I asked for the price. He punched 4.300.000 on the calculator, indicating 4.3M won, not 430k won That would have been instant buy if one zero was missing.