Trump is less vulnerable simply because he's not as repugnant of a person as is Hillary, not even close.
Trump is less vulnerable because, as a billionaire, he can ensure that any disagreements are settled in civil court. As a private citizen, he can ensure that non-disclosure agreements are part of any legal settlements. Clinton has been under the political microscope, which is only just now focusing on Trump, for 30 years.
He can parade a group of women (that he, himself has called unattractive gold-diggers) to accuse Bill Clinton of sexual assault, while holding his own set of allegations paid to go away hidden. Her on-camera statements are all authentic, deeply held beliefs. BS he says during interviews is all just a public character played for ratings.
He can hold up any government misjudgement in the last 30 years and put it on a Clinton. Government is big, some of the decisions are life-or-death, the consequences are very public, and hindsight will show those mistakes. Trump's own misjudgements, whether they're failed businesses, unpaid contractors, or just plain fraud, are basically private and mostly hidden behind layers of incorporation and settlement-without-guilt. A billion-dollar casino fails - that's just business; really only affects a few hundred employees, and they all just go get new jobs. Maybe they sue him for $0.10 on the $1. Failure was probably more due to the incompetent managers he hired than to his own decisions, anyway.