Although I think there might be some benefits to this style of government, I also think people over-index on it. One way or another these groups end up forming coalitions and making compromises in order to govern. In one case it happens before the election, and mostly behind the scenes with some influence from the primary process. In the other case, it happens after the election when the parties are figure out how to form a majority after the representatives have been selected. One advantage to the former is that at least you know who what other policies your special interest are going to align you with ahead of time, rather than finding out after the fact that your vote brought along more baggage than you bargained for.
> You and your friend might disagree about UBI, or trans rights, or whatever, but you both understand that you more or less agree on the other 9/10 issues.
But if one the people in that discussion is trans, and the other person doesn't believe that trans people are real, have a right to exist, deserve health care, etc. then it doesn't matter if they agree on 9/10 other issues. Same with abortion. If one person in a discussion believes in the value of rational evidence based decision making, and the other believes in woke 5g space lasers, there's simply no foundation on which to build a shared understanding upon which to base a conversation.
Many of the central arguments that are causing polarization in politics today are due to fundamental incompatibilities in values- the kind that no amount of agreement on other matters of policy
> Contrast that with american politics where it's all or nothing. If you like abortion and low taxes, there is no way for you to vote.
There absolutely is. There's no perfect candidate, but there's still going to be a better choice. You pick what matters most to you, and how many things you are willing to compromise for those things, make the best choice available, and work to push the discussion of one party or the other closer toward your views in the areas you don't like.