If a founder is only being nice to someone because it's a good idea and in their interest, they are an asshole. It's not a lesson you should need to teach anyone.
More generally, it's quite hard to find good <anythings>. People assume that available talent fits some sort of bell curve, with lots of 'average' people out there, but really it's more like an inverse square curve - there's a lot more people at the bottom end than the top. When you find the good ones you're nice to them because it's in everyone's interest.
Why do you have to differentiate being nice to people based on their abilities in any way at all?
Perhaps I'm misunderstanding your point?
Like the discussion of employee talent vs qty graph shape, there exists a similar graph of employer quality vs qty of some shape. And if you know as an employer you're at a very low point of that graph, unable to execute, unable to meet deadlines, unable to pay contracts in full, all you may really have left is nice personal charisma, making it all the more crucial.
You can behave like IBM or Google if you're IBM or Google. Little startup, maybe not.
If all you've got left is the ability to be nice because everything else is lost, then being nice is becomes more important than at Accenture or insert any other large company.
Its similar to the concept of "grace under fire" which used to mean something other than a sitcom or a martial arts TV show.
Being nice to someone isn't the sum of all time, money and energy expended on someone. It's just treating them with respect and dignity when your path crosses with theirs.