"The Founding Fathers could have never envisioned how riddled full of ideologues and despots this body would one day become and how injurious it would then be to this nation's long-term well-being."
I think they did. They had knowledge of European history, after all, going back to the Romans and Greeks. I'd wager they knew that government attracts despots, power-freaks, ideologues, and so on.
The checks and balances and limited government power the founders built into our government were, I think, designed such that even with a legislature riddled with despots, the real world outside DC had a good shot of running basically decently over time. And I think it mostly works.
(Heck, compare it to France, where relatively unrestrained government has the power to enforce socialist policies that cause an unemployment rate of 23% for young men... just exactly the demographic you want to be puttering about with too much free time.... Yeah, that's a recipe for social stability.)
Further, I think the founding fathers envisioned that things could, despite all the checks and balances and power limitations, end up even worse. Thus the second amendment.
They probably would have expected that revoking the states' authority in the Senate would have pretty much exactly the effect it did, which is they they tried to forbid such a thing from happening.