Which to me indicates that there was probably no documentation made if they did happen, so it would be impossible to audit like two years later, because being ignored when she told someone about the sexual harassment was one of her complaints.

When a law firm does an internal investigation, it's about judging the risk to the company if things were to go to court and not about if the events actually happened. So things like a lack of documentation is exactly what they are looking for. By using someone that can be considered to be a neutral third party, they can get the accuser to divulge whatever evidence they also have. You're not lying, the firm isn't there to make you look innocent, but you are clipping the leverage of the accusing party.

So, if the accuser says that they have a journal, or witnesses, or recordings, then you as a corporation then act to stop them from pressing forward. You fire someone, you pay them out, you say "oh, if only I knew about this we would've done something sooner", etc. This generally costs less than actual court and what would be ruled against you.
If the accuser has nothing, and you also have nothing that would shake loose in an actual investigation for your requirement to provide a safe workplace, then you can say things like "look, we paid someone to look into things, and it is looks like we're all good. We're going to put some policies in place to make sure that IF something like that every happens, that we can...."

It's like a voir dire without the actual trial. If things go to trial, well, you already know what your defences are.

'We paid someone to clear ourselves and they found nothing wrong' is my favorite business move.

I would likely in turn ask what makes him a bad person?

As I alluded to I have plenty of criticisms of him, but does that make him a bad person? Maybe using the terms "good" and "bad" are a bit too binary. Like a lot of things in life those terms can be at least somewhat subjective and most people exist on a spectrum. Most people however don't have large portions of their personality exposed to the world to see, nor do they have the livelihoods of over 100 people relying on that personality. I know for a fact that if my personality were broadcast to as many people as his is there are plenty of people who would take issue with certain aspects of it.

As to why I don't lump him in with people like Elon Musk or Jack Welch? He doesn't strike me as being a complete self interested sociopath. He seems like he is usually trying to do right by those around him and that he does care about those people. For example the turnover rate at LMG is very low in comparison to other related industries. If he were that terrible to his employees it's pretty hard to retain people as smart and talented as a lot of them are if they don't like it there.

I could come up with a lot of examples where he made some pretty bad decisions or how he doesn't know when to shut the fuck up, but does that make him a bad person? At worst he strikes me as someone a bit brash and ambitious that got really lucky before learning how to temper that and is now having to learn it as he goes along while sometimes being in over his head.