This is just not true. Both Trump and Clinton had some of the most unfavorable ratings of a presidential candidate for a major party in recent history.
You are correct that favorables of both candidates were low. But when you run a negative campaign, and Trump ran the most negative campaign ever, you drag your own ratings down as well. It was his only chance.
Exactly, they're both unlikeable, and if either party had nominated someone who was likeable, they probably would've crushed, rather than the dead heat we got in the popular vote.
Yes, when Trump ran his negative campaign, Hillary's favorables declined. Cause and effect.
In fact, using your own cite, if you run that back to 2015 and before and she has net favorables. The only thing you've shown is that negative advertising works.