Business is hard. If Trump was a really bad businessman, (Lots of examples, like this guy https://en.wikipedia.org/wiki/Mike_S._Zafirovski who was responsible for the ultimate destruction of a multi-billion dollar corporation) he would have lost all of that inherited wealth, probably from easily avoided mistakes.
Six of the companies Trump has managed have filed for bankruptcy:
1991 - Trump Taj Mahal - 3 billion in debt
1992 - Trump Castle Hotel & Casino - $550 million in debt
1992 - Trump Plaza Casino - $338 million in debt
1992 - Trump Plaza Hotel - $550 million in debt
2004 - Trump Hotels and Casinos Resorts - 1.8 billion in debt
2009 - Trump Entertainment Resorts - 1.2 billion in debt
Trump has presided over a surprising number of other business failures too (some of which he's still paying off lawsuits on):
Trump Steaks
GoTrump
Trump Airlines
Trump Vodka
Trump Mortgage
Trump: The Game
Trump Magazine
Trump University
Trump Ice
The New Jersey Generals
Tour de Trump (To be fair, nobody makes money on bike rarces)
Trump Network
Trumped!
I'm certain that Donald Trump would agree that business is hard. I'm not saying that he's the worst businessman ever. . . just that there's little he has done showing above average business acumen. When you say "Well, he didn't lose ALL of daddy's money . . . therefore he must be an OK businessman." I'm not sure that I can agree with the sentiment.