It’s probably more than “reliant on good-faith actors”. The Perils of Presidentialism by Juan J. Linz in 1990 is a decent paper comparing the instability of parliamentary democracies vs presidential democracies. Parliamentary democracies aren’t perfect, we have Hungary, but in hindsight it shouldn’t be surprising that presidential two party democracies are unstable. If you get two ideologies that are different enough then the government swings between the ideologies with the executive pushing for its side and opposite side getting angrier until, after a few oscillations of increasing amplitude, something snaps.