Im excited to see one of these i can answer on, if my formatting has any errors or if any clarification is needed let me know, this is my first post here :)

The last ruler of the shang dynasty was Di Xin, most commonly known as King Zhou. As for your specific question about how many of his dastardly deeds are fact or fiction: I personally believe that it is mostly exageration with a basis in fact.

There is evidence that he was truly a corrupt leader. The best resource to answer your question would be the Shiji by Sima Qian, written around 100bc. Sima Qian is well known for attempting to be factual and will often make note of sources or if information is unverified.

Sima qian makes direct reference to king zhou doing these things: torturing criminals with burning coals, imprisoning the lord of the west for fear of his good reputation, releasing said lord when bribed with women and luxury goods, killing his advisor prince bigan (the uncle you mentioned) by slicing him in half, and imprisoning his advisor prince ji(another uncle). He is also mentioned to have fallen into extreme depravity towards the end of his reign and to have allowed his ministers to completely suppress his people for corrupt gains. Overall he is painted exactly as you mention: violent, alcoholic, sexually perverse, swayed by profit rather than virtue and abusive of his status to extremes.

However, there are three points that i think are important to consider when analyzing this account: King Zhou’s relationship woth the Lord of the West, the Zhou dynasty influence on this account, and confucian influence on this account.

The first two points are closely tied together so i will begin with the third: King Zhou was written about directly in the analects of confucius, in fact some of the exerpts in the chronology written by Sima Qian are direct quotes. The analects pulled upon the tale of King Zhou as a pefect negative example of what a king should not be. In case any readers are not aware, confucius belief is based on the idea that how well a country does is based on the moral standing of its people on very specific subjects. It also believes that this moral standing begins at the top of the pyramid with the ruler of the nation being virtuous. Knowing this, it becomes clear that confucius thought is far more likely to paint King Zhou as a parable of evil than as he was in life.

As for the first and second point: zhou influence on the recount. When reading about the tale of King Zhou it is clear that the Lord of the west King Wu is the “main character” in the tale, and King Zhou is the perfect foil to King Wu’s virtue as a perfect king. When prince Fa rises against King Zhou to begin the Zhou dynasty he is written as if destiny is on his side, carrying out the will of heaven to strike down evil. I think it would be perilous to ignore the strong possibility of the old adage coming into play in this tale: the winner writes history. There is a big possibility that King Zhou’s decadence was exagerrated when he was written about by the lense of the zhou dynasty’s influence. The fact that the lord of the west king wu and prince fa are subtly referred to as the true beginning of the zhou dynasty is another attestment to this fact.

So while all accounts point to King Zhou was a bad king, it is hard to take the tales at face value.

As for the the lake of alcohol i believe this to be a poetic embellishment, perfectly in line with the chinese style of story telling to emphasize King Jie of Xia’s opulence (what alcohol was a symbol of at the time).

I made references to the Shiji and other works through the lens of Dr. Robert Eno’s translation and studies: viewable online in part here and here

Edit: it is midnight where i am, i will add to my sources tomorrow.

Related question if it's allowed:

Would this dude's behaviour have anything to do with his being the dynasty's final ruler?

Any sources for reading on this?