One can only wonder how much thought and sophistication goes into maintaining this hack.

Most of cyber attacks begin with phishing; this attack aslo began with spear phishing if I remember correctly from reading news headlines and research papers. They got in by phishing and then they emptied Bitfinex's hotwallet. It happened so many times in the history of Bitcoin and cryptos it is not even surprising anymore nor sophisticated.

I think the "maintaining" is the key part here. Now that the hackers have the coins, how do they do anything with them without getting caught? How do you continue that over years and years and years?

Yeah, that's what I meant with my original statement.

I am thinking of comparing this to something like winning the lottery, like millions worth of free money. I think the contrast to acquiring such large sums of money illegally is pretty high.

Like, I don't think this person or group of people are able to live their lives and not constantly think about it.

Funny enough it is easier to launder cash than Bitcoins because shadow banks can help you to launder cash, on the other hand with Bitcoin everything is on chain forever.

But wouldn‘t any Bitcoin Tumbler just break that chain link? I guess 3.5B are gonna be a pain either way, but at that scale cash has much bigger logistical issues.

Kind of, but not really. The tumbling transaction is itself public. If anything, this would spread the taint to all other outputs of that tumbler, not remove it from your own output.