I don't know that Singapore (effectively a single-party state whose PM has dictatorship levels of power) is the best example of how this works in a republic (or sub-republic) with separated powers.
Every major democracy is effectively a two party system. Further, both parties are usually quite corrupt, despite claiming to be the opposite of the other.
Even granted that, in a (n>1)-party system there is the capacity for electoral repercussions for individuals who demonstrate extraordinary corruption (as in the situation we are discussing here). In a single-party unitary system, there isn't even that possibility.
