1. As the previous response notes, Hillary was running against one opponent while Trump was running against many more, anywhere from 3 to 10 or more. But in addition to that, Hillary has piled up the biggest part of her vote total lead against Bernie Sanders, maybe more than 100% of that lead, in states that a Democrat, whether Hillary or Bernie, is unlikely to win in a general election vs. Trump.
2. Every election is the most important we've ever faced and you can find quotes on every one of them. It does nothing to distinguish between Hillary or Bernie versus Trump.
3. This answer illustrates how many different points of attack Trump would have against Hillary. Add in political positions she is vulnerable to be attacked on by Trump that Bernie can't be attacked on: 1) support for Iraq War, 2) support for every free trade deal, 3) vast sums pulled in from SuperPacs, 4) close ties to Wall Street including speech income. Those are a few, I'm sure there are many others. Bernie can be attacked by Trump on the socialist label and on being too far left, but as Hilllary's campaign has found out there isn't a whiff of scandal to pin on Bernie. The only attempts she has made to go after Bernie on his voting record have blown up in her face.
4) A long winded example of name dropping and a replay of the 3 AM phone call ad. It can be easily countered with her hawkish past as a supporter of the Iraq War and as Secretary of State.