Honestly, this sounds a pretty big misreading and/or mis-characterization of the founding fathers. What's important to know about them is that, the majority that we know by name, were concerned with property rights. Indeed, one of the primary cause of the revolutionary sentiment was a perception, mostly thanks to the Intolerable Acts, that the Crown did not respect some of the common rights that British people had enjoyed for many years in their colonies, and those rights centred on the control over one's own property to do with as one saw fit. If we wanted to get a little abstract, this same sort of sentiment also had a large hand in the Civil War. It should be seen as no coincidence that so many of the rights enshrined in the first. For sure 2/10 (3rd and 4th) are about property rights, and indeed, are direct responses to those Intolerable Acts. Several other of these can also be construed to be about property rights as well. Ultimately, most of these men were exceedingly wealthy, and democracy in the United States was still a descendent of that found in the United Kingdom; that is, one primarily founded by a movement of wealthy landed men against the 'deprivations' of the crown, mostly on their property rights. In this sense, the American Revolution has a lot in common with previous resistance against the Crown over the previous centuries back in Britain.

That said, I don't think that there's any good evidence that those framers were interested in a system that would keep people 'down'. Rather, they were simply disinterested in a system that would raise people up. Some justified this, as Jefferson and Madison were want to do, as a defense against expansion of the government (and thus a reduction in the freedom and powers of the citizens underneath it). They were first and foremost concerned limiting the power of the government (sometimes to a fault) to enact the kinds of deprivations on them that they felt the British had. A quote, from Thomas Jefferson: "A wise and frugal government… shall restrain men from injuring one another, shall leave them otherwise free to regulate their own pursuits of industry and improvement, and shall not take from the mouth of labor the bread it has earned. This is the sum of good government.” You can see here that for Jefferson, the crux of good government was protecting labour and the fruits of those labour from criminals, and the government itself. This wasn't a conspiracy, but simply a reflection of centuries of development that took place in Britain and was transferred down to the colonies. The constitution represents the ultimate victory of the ideals found in the Magna Carta and Lockean political ideals. In a way, the author of the essay is correct; the constitution was built to protect the powerful oligarchs, but only in so much as it was built to protect the thing that made those men powerful: their property. There is nothing explicitly in the constitution preventing others from gaining property and thus power under this original framework, other than inertia.

That, some certainly worried that the current state of affairs as it existed was not sustainable, and saw the risks in how the state was set up. James Madison, for example, despite his general opposition to the idea of wealth redistribution, had this to say about the risks of a state where many are disenfranchised by their lack of wealth:

"If all power be suffered to slide into hands not interested in the rights of property which must be the case whenever a majority fall under that description, one of two things cannot fail to happen; either they will unite against the other description and become the dupes & instruments of ambition, or their poverty & independence will render them the mercenary instruments of wealth. In either case liberty will be subverted; in the first by a despotism growing out of anarchy, in the second, by an oligarchy founded on corruption." Emphasis mine to reinforce the point above about property rights.

The issue for most of these men is that, by giving the government the power to start picking winners and losers, they feared (as the quote above illustrates) that that power would fall to a corrupt oligarchy interested in power, not democracy.

As an aside, I am not a libertarian by any means, but if anything, I'd argue that Madison's prophecy above is way closer to reality today thanks to the expansion of government. The things that this author is blaming these men for is something they were trying to prevent. I don't think they succeeded, but there it is.