Unfortunately, it’s not quite that simple, at least when it comes to national-level US politics. I’m a registered democrat. I’d say my view is closer to D than R on about 80% of issues, which is sufficient for me to happily identify as a democrat without constantly having to throw out qualifiers and addenda and so forth.
Nonetheless, I can certainly imagine an election in which I thought that the Republican candidate was just better, more qualified, more sensible, less corrupt, more in-agreement-with-me, than the Dem candidate.
Unfortunately, for any of the prominent federal positions (prez, senator, congressman), there are ripple effects which would make it VERY hard for me not to vote for the democrat. In congress, the party that has control of congress is MASSIVE, as we have seen with the reign of awfulness of Mitch McConnell. Even a GOP candidate who I greatly respected would, assuming they are GOP enough to be running as a GOP candidate, caucus for McConnell as majority leader. That’s a MASSIVE factor, quite possibly as large a negative (from my perspective) as whatever benefit I would get from having a senator who I genuinely liked and respected.
As for presidents, there’s the issue of supreme court justices. Now, I agree that that’s not 100% a slam dunk. If there was a candidate who I thought was a revolutionary thinker who identified as GOP but basically had a unique and personal political philosophy, which I thought was super awesome, then maybe he would nominate SC justices who followed his own political philosophy. But in the much more likely case of “sure, candidate A is a dem and candidate B is GOP, but candidate A is lackluster and corrupt, and candidate B is brilliant and I totally respect them”, the fact that candidate B is still nearly certain to nominate conservative justices, and the longlasting effect of that, means that I would still likely vote for the democratic candidate.
And, frankly, I think that’s a shame. I think it’s a weakness of our system. I can certainly see the original intent of the checks-and-balances and entwinements between the prez and congress and the SC (SC nominations, having to sign laws, vetoing), but it does make it VERY hard for me to not vote for someone of “my” party. And it’s not because I’m a mindless team-playing sheeple, it’s because that’s what the system motivates me to do.