You are not wrong in some things here. He is absolutely a moron. A power hungry child who doesn't know what to do with the ball once he's been given it.
Here's where you're wrong.
They don't want Trump because he'll do all these things on his own. They want Trump because he will do whatever he's told buy the voices he believes. He is just the tool. The power lay behind the throne, so to speak. He is surrounded by vile people who tell him what he wants to hear and in return he signs his name to whatever they want. And that is how he accomplishes the sort of things people are afraid he will.
He is a tool, nothing more. Unfortunately he's an effective one.
This isn't an untested proposal.
Trump had a slight majority in the Senate and a slight majority in the House for the first half. He vetoed 9 resolutions, which are largely meaningless. Congress giving a public opinion and the President saying he disagrees. He vetoed ONE bill, a regulation on fishing nets. So legislatively speaking, he was pretty much a rubber stamp on a very tight Congress. He had two things that he was leading on: Restructure of the tax code and border wall. The tax bill was popular with GOP in general and would have passed with any GOP President. The border wall made some progress, but couldn't keep approval when Democrats got the House and he had to amble on a bit with funds he could find other places and between that and other laws and court issues stopped him from finishing the job.
He put 3 conservatives on the Supreme Court. Kavanaugh is a bad person and got resisted for that reason, but he was a high level Appeal Court judge already, would have been shortlisted by any Republican and he's been a pretty standard conservative Justice like Gorsuch and Barrett whose presence is resented, of course, by progressives but are predictably and boringly conservative. The conservative Justice that is still and increasingly the biggest pill was nominated by George HW Bush. I am not so familiar with the appointments he made to lower courts. There were lots of openings because the Senate had blocked Obama, but I understand that Trump's appointments below were similarly from pretty conventional GOP recommendations. Judges that were conservative, but had the correct resume and credentials. The same ones that any Republican would have been choosing from.
Granted, in the time that he had the House of Representatives, he also had deeper GOP-side staff in the White House that obstructed him. By the time he figured that out and mainly filled his staff with sycophants, he had lost the House. I'm not sure how much those things line up, though. The GOP-side staff were not stopping him from signing bills that the GOP Congress sent to him. Once he got his more sycophantic (<---I don't know if that is word) staff, the sorts of things that dark voices want him to do are not legislative. The crazy things that are whispered in his ears are difficult to pass through Congress. We won't see a 60-40 Senate again until some major issues shift and a majority in the House isn't what it sounds like. They are fickle and a lot more diverse. And they debate it all publicly and make headlines. They don't want to crazy things that the President asks for. They want to do things that are popular with their constituents.
\He has always done a lot of damage by talking and he was able to do more of it when he was the actual President, but he did this before he was President and he has continued to be able to do it afterward, especially thanks to having been President. He will continue this whether he wins or not.