I disagree. They were certainly familiar enough with English politics to recognize the not just the possibility, but the actual likelihood, of career politicians.
And we should note that a long political career is not necessarily a bad thing, though we have plenty of evidence that it's quite often a bad thing. The difference between good and bad is, of course, the quality of the politician himself.
I think Madison and Jefferson probably made the mistake of assuming that there would always be more "good" than "bad" politicians -- something I imagine they believed would be protected by the requirements for land ownership among voters, and indirect election of senators. They probably also assumed that the political class of future generations would generally have the same extraordinarily high quality that characterized the Founders' generation.
I think that Franklin was a much more cynical -- and thus more realistic -- judge of human character than Jefferson ever was (I can't knowledgeably discuss Madison's views on the topic).
Franklin probably had the proper understanding of the nature of man, while others often do not.
The nature of man is NOT “basically good”.
Actually, I think Madison and Jefferson thought that our electorate would remain an informed and moral electorate. And that said electorate would easily get rid of the bad politicians.
Unfortunately, with the communist control of our education system, we now have an electorate of brainwashed, immoral idiots. That allows the bad politicians to bribe them with goodies from the public treasury for continued power.