the founders knew how politics worked. by the turn of the 19th century, all of what you ascribe to the 20th was in full effect. the Rs and Ds have dominated politics since the 1850s. color me baffled.
an anecdote:
"Men by their constitutions are naturally divided into two parties: 1. Those who fear and distrust the people, and wish to draw all powers from them into the hands of the higher classes. 2. Those who identify themselves with the people, have confidence in them, cherish and consider them as the most honest and safe, although not the most wise depositary of the public interests. In every country these two parties exist, and in every one where they are free to think, speak, and write, they will declare themselves. Call them, therefore, liberals and serviles, Jacobins and Ultras, whigs and tories, republicans and federalists, aristocrats and democrats, or by whatever name you please, they are the same parties still and pursue the same object. The last appellation of aristocrats and democrats is the true one expressing the essence of all."
-- thomas jefferson ...in a letter affirming his view on the facts of partisan politics.
I think we're talking about two different things here. You're addressing a letter from Jefferson, a known proponent of partisan politics, opining on the coalescence of the two basic ideological camps originating with the Federalists and Anti-Federalists into groups and an identity being attached to each group. I'm talking about the formalization of those groups into the modern partisan entity and the formation of the current public welfare system propping up and protecting those organizations from competition - and themselves.
One is a more or less natural occurrence (assuming each of these "parties" can naturally be gathered under a single umbrella - as the struggle among partisan factions illustrates is not necessarily a natural occurrence in itself) and was addressed in one of my earlier posts, where I stated I have no problem with a two party system per se so long as all players are given a level playing field and free choice.
The problem I have is not with people voluntarily organizing, or forming parties, or any other group of whatever name you want to apply - grassroots movements and the like. That's association. The problem I have is with the modern system wherein the two main parties are given systemic preferential treatment and all potential competition is squelched, by official means such as decertification or higher ballot fees as well as unofficial but just as damaging means such as being blocked from access to candidate debates.
I am disgusted for example by any system that allows private organizations to choose their club's approved candidates by public ballot, but then may close those elections to all but their own club's members claiming they are Party events - and hold a hand out for the States to administer and finance them. Or by laws on the books such as those in the OP, that place higher threshholds for ballot access on minor parties or nonpartisans and attempt to pretend it's anything but favoritism. We cannot have a religious test for office, but we may have a partisan one to even get on the ballot? It's irrational.
I disagree completely with the assertion that the system is in any way dependent upon a formalized two-party political process with two publicly protected, lockstep voting blocs in order to function. For every Jefferson, a known partisan, there was a Washington, who is famous for his distrust of formalized political parties. There was no consensus on a formalized, coddled, protected two-party system to run the goverment they were creating.
The system is designed with more than one basic tension reflective of the compromises inherent in its design. It just so happens only one divide is reflected in modern partisan politics - so we tend to miss the governing and systemic nuances in favor of partisan tactics. "Red" and "Blue" are artifical constructs, there is room for a rainbow of colors in the issues out there as there were among the Founders themselves.