Just because Congress is stuck doesn't mean the Executive gets to do whatever they want.
What happens when things aren't stuck, they change too much, in both frequency and magnitude. Kind of like when one person in the executive branch gets to make the rules. It's utter chaos and uncertainty on the business environment, even on the consumer environment, they have no idea what anything costs anymore. Am I paying double from a year ago because of tariffs or because it's easy for the seller to say tariffs, I'll never know. As a business, should I charge more now in anticipation for future uncertainty, has seemed simultaneously unfair and prudent. Now, should I reduce prices to go back to pre-tariff or just pocket it and call it inflation. Uncertainty is chaos, it's hard to plan for anything or make big decisions. This is why high(er) rates didn't hurt the housing market but all the Trump related uncertainty did.
The executive branch is less accountable than the legislative one. You elect only the top office, and only once every four years. With so much bundled into a single vote, it's nearly impossible to hold any specific action to account.
It doesn't work out great for the judicial branch, either. They often rule that a decision is based on the law as written, and it's up to the legislature to fix that -- while knowing full well that the legislature can't and won't. And they're not consistent about that; they'll also interpret a law to favor their ideology, and again Congress is in no position to clarify the intended interpretation.
Congress was deliberately set up to favor inaction, and not without reason. But that has reached the point where it practically doesn't even exist as a body, and its ability to serve as a check on the other branches has vanished, leading to even more abuses.
Vote the GOP out, and he'll be impeached.
And I don’t think a multiparty system would have been able to stop the rise of Trump all else being equal equal.