I certainly agree with your comment, but possibly you didn't see the quotes around my use of the word 'required'.
But then again having monitors at all might not be 'required' to get a good mix, you get really lucky.
I would contend that most any set of reasonably wide range speakers can be used to create a good mix.
With a lot of luck, yes. At least to create as good a mix as you could with better equipment skill level being equal.
You are correct in that you can account for known problems in speakers but this is FAR from exact science, no matter how good you are at it. The less you have to depend on this the better off you are. If I was to use my wife's computer speakers for a mix compared to my Event TR8s there would be a NOTICEABLE difference, despite the fact I have probably even heard my wife's speakers more than my own monitors as I fall asleep listening to movies playing out of them and my studio I tend to work in a couple times a week at most, depending on where I am in a show as I spend a lot more time working elsewhere, either in meetings, collecting sounds, wiring systems, or even using the system in the space.
All that being said I wouldnt touch her speakers for a mix as I know how bad they are, I know their frequency response, and I know that even if I attempt to compensate for it it wont be as good as my monitors for that purpose since I dont have to struggle to compensate for this by memory.
Seablade