When AD is on TV, he oft times has a limited amount of time to respond to questions, due to the massive number of talking heads now recently popular on these cable TV news panels.
With those time constraints, Dershowitz makes his main points without going into every possible scenario and possibility. You well know some of these highly technical legal and constitutional discussions could be debated for hours, but when Don Lemon, Anderson Cooper, etc have 7 or 8 guests on with him, nuance, subtly and detail are often casualties.
But when he is pressed on the subject, he has acknowledged that Trump can commit OOJ, when as you say, he commits an "independent crime."
As your link points out, when AD has more time/space to delve into the topic more fully, he has stated that the "corrupt intent" component is flawed to bring action against Trump, especially when he is otherwise acting with a power awarded to him by the constitution.
He also points out, as the staunch civil liberty defender that he is, regardless of party, that it is virtually impossible to determine what Trump is thinking, again, when considering he is acting within his constitutional power.
So of course you, and others may disagree with his assertion, but to state categorically that he is "wrong" is incorrect as you both are stating your opinion on what is essentially an unsettled constitutional and/or legal matter.