I personally don't think it's fair on the rabbit. Rabbits are social creatures, and even with the best intentions in the world and the most dedicated effort at spending time with an outdoor bunny, it's never realistically going to top 4 hours company a day at most...and in reality for most people it's going to be maybe half an hour to an hour, especially in bad weather! So that means that a naturally social creature will be on its own for at best, 20 hours per day, at worst, nearly 23.5. So for the vast, vast majority of the time, the animal is going to be on its own. Visiting twice a day to feed, stroke and clean out just isn't anywhere near enough, IMO.
At least as a housebunny, the rabbit will get interaction when the owners are at home but not spending dedicated time with the rabbit - having breakfast, preparing dinner, watching TV in the evening, doing the ironing etc. It may not be perfect, but it provides the bun with a whole lot more company and interaction than being outside alone.
Yes, rescues might do it...but there it's a temporary thing with a better long term purpose. Most decent rescues won't rehome single rabbits to an outdoor home, for this very reason. It's one thing for it to be the case for maybe 6 months while the bun is at rescue, but it's another thing for that to be the case for an entire 7-10 year lifespan.