I think it depends on the rabbit and the circumstances. First is if the rabbit will even bond with another rabbit. There are some rabbits that seem to hate others of their kind. So it could be very difficult to find a rabbit with a personality like this, a compatible bunny companion.
Then it has to do with the rabbits living situation. If the rabbit is outdoors(or indoors too) and only visited a few hours or less per day by the owner, or doesn't enjoy human company, then yes, it would be best to find a rabbit like that a compatible bunny friend(both spayed/neutered) to bond with. If the rabbit is indoors, likes to spend time around people, and gets several hours a day quality time spent with people, then I think a single bun can do fine in those circumstances.
The differences in recommendations you're seeing, may in part have to do with the location of the person giving their opinion. Generally in the UK and some parts of Europe, rabbits are often kept exclusively outdoors, so for those rabbits it is better for them to have a bonded companion, as generally most people don't spend several hours outdoors each day with their rabbits. Here in the US, the main push in pet rabbit sites is for rabbits to be kept indoors. And indoor rabbits when given a lot of quality time with their human companions(where the rabbit enjoys human company), can be perfectly happy with that.
So as long as a single rabbit is getting lots of human companionship and behaves in a manner that shows it's happy with this living situation(not just hiding out alone by itself most of the time), then my opinion is there's nothing wrong with this.