Yeah it absolutely isn’t the only factor, but it’s one of the biggest ones. I neglected to point out it isn’t the only factor.
After FPTP issues, the next biggest one in my mind is the spending rules. I think that all candidates should operate from a “shared pool” of election funds. So if candidate A wants to use 1 million for the election, half of it goes to them, half of it goes to their opponent. No candidate should have a higher spending fund from another. It would drive down campaign spending, make bullshit political ads less frequent, and add a degree of fairness.
That, and there needs to be a full ban on lobbying (read bribery).
As for the few elections in southern states that use run offs, that’s not quite what I’m looking for, and those elections aren’t in a vacuum. The political power the two parties get from surrounding areas is enough to mean 3rd parties still don’t have a chance.