To be fair plenty of real world politicians have dealt with the criminal underworld, extorted people, and had undue influence over law enforcement.
Fisk, to me, is played as almost an anti-villain (defo not the right term but until someone tells me the right one I'm using it). He is clearly not a "good" person but he is a very principled person with a strict morale code and I think he genuinely does believe what he is doing is for the ultimate benefit of the city as a whole even if he has to use unsavoury methods.
You can almost see at times that he is conflicted by the choices he feels he has to make - and has taken on the "martyr complex" whereby he doesn't believe anyone else will do or can do what is necessary to achieve these righteous goals and so takes it upon himself to do what others can't.
He is a really good foil for Matt Murdock - both charming in their own way, both with a strong sense of right and wrong, both trying to make the city a better place, and both with a very deep and dark side to them only Murdock's choices are presented as being "more right" than Fisk's (and mostly are) but this version of Matt is no saint.
I'm sorry, have we seen the same show, especially after the finale?
I have to disagree hard on your take. Fisk is a villain, plain and simple. Villains can be principled too in their own way but this doesn't mean that standing by your word or making a fair deal for both sides means anything if it's illegal.
I mean the parallels to Trump are not very subtle - a criminal enters politics and despite the odds wins only to continue using his criminal methods but on a larger scale now.