>has identity politics has been shown to be such a loser for republicans?
Pretty much, which is why they didn't really do it. Trump stole from Bernie's playbook - if you take his last few ads as a representative sample - they pushed the class warfare angle pretty hard - starring Lloyd Blankfein, ironically enough.
That played really effectively off Hillary's "business as usual ; government is hard ; I work hard" angle, and was probably responsible for her losing Michigan - not exactly a state that has done well out of the status quo or the trade deals she championed.
>2) since more people voted for Hillary than Trump, is "universal" loathing actually a problem for presidential candidates?
Yes, because the numbers that stayed home in disgust outnumbered both candidates. Voter turnout is what killed Hillary's chances, not "white supremacists" or "fake news" or whatever, and that voter turnout was because she was such a thoroughly loathed individual - which was actually largely her doing.