I don't see a lot of people arguing that trump isn't as bad as Biden. The argument I see (and one I subscribe to myself) is that Biden is better at being bad. They're both horrible ghouls that would murder a child for a nickel, and they can at best be said to be indifferent about various causes.
The argument is that Trump was incompetent. While he attempted to suppress minorites in the US he saw massive nationwide demonstrations in response. He tried to antagonize Iran, but failed to escalate the situation to anything that didn't just make him look foolish and wasted precious US resources. Attempts like seizing Iranian tankers were widely condemned, which caused further cracks in US soft power. The world as a whole started to distance itself - The Korea's started peace negotiations without the us, and South America turned leftward. His needling in Venezuela failed, his coup in Bolivia was overturned and the US stooge that was got kicked out after a short while, to be replaced with .
It's not that he didn't attempt these things, it's that he failed. Meanwhile Biden has seen the overturning of Roe v Wade, increases in transphobic laws with little to no resistance from the general us population, and a war in Europe that put the place at its heel. He escalated tensions with china early on and elsewhere the meddling of the American empire can once again be felt.