How do 10 very different mods all fill the same niche?
They all play their part in filling the corners of the niche, so that the niche as a whole is filled.
That's not how i think of it. I would say the the usefulness of video games is that they're entertaining.
Please try to convince literally any school of that.
I mean, it's pretty simple: people need to be happy in order to be productive.