It's important to keep in mind that the older generation that needs to be supported right now and the generations before had plenty of kids and the problem does not exist at the moment - it's more about what happens if the trends holds and the generations that are at well below replacement rates start retiring.
Also, most of the wealth held by the top of the wealth pyramid is not what has already been produced, but merely claims on future production. I doubt people at the top of the wealth pyramid consume all that much as a fraction of the society's productive capacity - either they are holding onto existing claims or creating new claims by making investments that would increase the future productive capacity.
So if there was a production gap and the youth is not able to support the older generation due to the lack of productive capacity, moving the wealth downwards would exacerbate the gap, because you'd be redirecting some of the productive capacity towards consumption rather than investment.
Also, most of the wealth held by the top of the wealth pyramid is not what has already been produced, but merely claims on future production. I doubt people at the top of the wealth pyramid consume all that much as a fraction of the society's productive capacity - either they are holding onto existing claims or creating new claims by making investments that would increase the future productive capacity.
So if there was a production gap and the youth is not able to support the older generation due to the lack of productive capacity, moving the wealth downwards would exacerbate the gap, because you'd be redirecting some of the productive capacity towards consumption rather than investment.