I don't see how it's a dichotomy.
It's entirely possible that a closed ecosystem enables a large number of features with a certain set of tradeoffs, and an open ecosystem enables a large number of features with a different set of tradeoffs, and there is overlap between the feature sets.
Does that mean that there is no need for an open ecosystem, when you can get what you need from a closed ecosystem? No, because while all the features you care about may be in both, the tradeoffs you have to make to use the closed ecosystem might not be the tradeoffs you want to make.
And the converse is equally plausible: That you can get all the features you care about in both, but it does not mean that there is no need for a closed ecosystem, because while all the features someone cares about may be available in both, the tradeoffs they want to make may align more closely with the closed ecosystem's tradeoffs than with teh open ecosystem's tradeoffs.
I think it is true that given some set of features, we can nearly always find a set of open source products/packages to deliver the required functionality, and for a very pedantic literal sense of "need, " OSS does everything people need.
But hardware and software products are more than just a set of features. They're the other tradeoffs that form a messy collection of affordances and pain points, and different people have different needs from the entire product's perspective.