We need a system that allows a freer market of political parties. With two entrenched private organizations that are impossible to unseat, an extremist takeover of one is like taking over the country... Which is what has happened. Imagine a system where rational Republicans could have formed a breakaway conservative party and had a chance at success without being a spoiler.
And I think the new voting system has to have preference built in. I know approval voting is simple to explain and calculate, but I want to maximize the "expression of voter preference" as much as possible while keeping the process simple. Ranked choice has some issues but it is conceptually simple and eliminates the spoiler effect. And it's already in use in parts of the US.