I highly, highly doubt that about tariffs. I mean, I used to think exactly what you're saying when he first started lying about them during his first term, but once I learned he was getting his ideas from Robert Lighthizer I started taking him more seriously. Not that I think he's following all of Lighthizer's advice--he clearly isn't--but he usually learns enough from the people he brings into his orbit to make up for the deficiencies you're pointing out which I agree are quite real and repeatedly surface. My assumption is that he took just enough of Lighthizer's advice to benefit himself, but I haven't figured out whatever angle he came up with yet. Did he come up with his $TRUMP meme coin himself? Of course not; someone pitched it to him as a way to take bribes, and he went with it. You can make up for your own deficiencies by surrounding yourself with smart people and stealing their ideas.
I still think Trump would have never been president if not for Steve Bannon teaching him the playbook he's followed ever since they met back in 2010. Trump has had a number of key influences that brought him to the presidency--Roy Cohn who he has repeatedly credited over the years, his lawyer Michael Cohen, Bannon, etc etc. Jesse Ventura claims that Trump stole his campaign techniques and has been using him ever since they first considered running together as a third party ticket around 2000.
In terms of his public persona he was always guarded in what he said even back when he was a regular on David Letterman or Howard Stern in the 1980s, and 1990s, but after he started getting political ambitions in the 1990s first with the Clintons and later with Jesse Ventura he seemed to learn to just completely be whatever he thought people wanted out of him to gain influence and power. We have only fleeting glimpses as to what the man himself is like anymore; 90% or more of what comes out of his mouth is manipulation of public opinion for at least the last two decades, and he was working on that behavior long before that.