So, at this point I realise you have noticed some things but totally missed others. On the other hand, I agree with you on something that many missed; il-nam was a complete and utter hypocrite. I don't just mean him dying, take this 'equality' stance he holds (or at least the cop's brother holds), there's no way at all they thought that by not punishing fighting that someone with a body like Deuk-Su is on equal footing with someone like Sang-woo for starters (and Sang Woo was a brilliant fighter and tactician but just face it, Deuk-su wins that fight every time).
What I am getting at here is that the very fact alone that beating the crap out of people, even to death, was unpunished within the resting area meant that regardless of one's ability at games, one was permanently a slave to one sole skill; hand-to-hand combat. No amount of social skills would help either because a 'gang' has every reason to turn on each other since only one walks away with all the money.
That is one main reason I don't despise Deuk-su at all, not even for how he betrayed Mi-nyeo (the chick he banged). At the point of betrayal, he had every reason not to jeopardise himself and his team and was nearly 100% certain her team was bound to lose given that the doctor had told him what the challenge would be and that the command for them to be teaming up made it more likely the doctor was correct about what lied ahead. He had to maintain a ruthless persona even if he actually had feelings for her (which I don't think he did but if he did, he'd have had to act extra ruthless anyway) and ultimately he got extremely unlucky with how things played out. He even correctly abused his strength in the glass game, I would absolutely do what Deuk-su did there, even if I was weaker than him. I don't even know why anyone bothered going, what you do is blackmail the rest to vote to end the games if you're an early number, if anyone tries to push you off, you grab onto them and kamikaze and say you'll do that beforehand. This would have led to the glass expert helping them a bit and may have led to a totally different outcome.
Regardless, I am saying I see what you mean about hypocrisy and double standards along many angles in the game but that didn't make me dislike the ending, that was something I noticed before that was revealed.
I also think you didn't pick up on many clues that Il-nam is actually the father of Gi-hun and obviously was a sociopath who didn't give a shit about his son but just knew who Gi-hun was and engineered encounters with Gi-hun (such as counting with his finger pointed just as Gi-hun passed by him though I think that was a genuine thing he was doing because he needed to know his brain could still count people accurately so he'd stop the night-fight just in time for four teams to be the amount left). When Gi-hun says he's lactose intolerant and asks for chocolate milk (both a ridiculous and yet reasonable request because chocolate milk still has lactose but yes, it has slightly less and the lactose itself fuses with the cocoa somewhat to make digestion a tiny bit easier, it's why lactose-intolerant people often react more severely to something like pizza than a chocolate)... Anyway, Gi-hun says that and then the old man asks him if he got beaten for that as a child, then Gi-hun says 'yes' and the old man says he did that to his own son.
Another clue to pick up on (there's clues that were so abstract you couldn't pick up on) is that when they run around the marbles arena it's based on the old man's house and Gi Hun specifically states that he himself remembers living somewhere like this (clearly before the divorce/split which led to his mother needing to move in with him). This may also explain why the old man spared Gi-hun in marbles at all but I doubt it. At that point Gi-hun had proven himself even as a non-son ally and the old man obviously had planned to be the 'sucker' that didn't get picked so he could easily leave without getting noticed, this was all ruined because Gi-hun decided to pair with him.
I am confused though, since had the doctor not been killed off prior to marbles, there'd have been an even number of competitors but perhaps the old man had planned to drag out the marbles game regardless and do it how he did so he'd be killed at the last second and be able to fake it.
What you say though, about his motive not making sense, is partly because I think Korean statements that are philosophical don't directly translate into English (both an issue on subbed and dubbed). What he was really saying was his motive, if you follow the context of the last scene, wasn't to just thrill himself, it was also to prove to himself (not the other businessmen involved) that at the core, humans are corrupt and that no matter how many random variations of people enter such a contest, they all end up backstabbing and selfishly operating regardless of what social bonds they form or previous assistance. I think he explicitly knew his own son was entering the contest that round, which he didn't mention to Gi-hun as he didn't know how to justify why he'd ditched him and his mother even financially despite being that rich. I also think he'd had Gi-hun followed long before and engineered it so that Gi-hun in particular got invited after he'd had every chance to get out of his parasitic lifestyle himself. This may explain why, sure others may have had many chances too, Gi-hun was already in crippling debt for years but only got asked to come to the game years after it began. He'd have been a perfect candidate way, way before. If you observe Deuk-Su's, Ali's and Sang-woo's backstory, those 3 explicitly are made clear to only have recently got into crippling debt scenarios, Gi-hun is in contrast shown to have perpetually been in it for years before he was asked to join the games. This is a much more subtle hint that Gi-hun was the old man's son as opposed to an ordinary candidate (as well as the old man seeing Gi-hun after quitting or even the old man voting 'no' when he was the tiebreaker, respecting Gi-hun's wish).
The one thing against this theory is that the old man who clearly had sussed out the honey candy game being what it was, chose to let Gi-hun get umbrella (initially he let Gi-hun pick and insisted on it but Gi-hun then picked the umbrella and insisted the old man confirm he was okay with star). I also think the old man even knew the licking method and that holding the candy to the 'sun' would give a significant clue (given what he says about stars) but what confuses me is why he'd risk his own son losing on that particular task. I get that he is a darwinist and believes if his son didn't earn the win he doesn't deserve it and wanted to give his son a fair chance in life but I don't get that one time why he didn't either take umbrella or suddenly 'remember' the symbols and say they should all pick triangle.
My explanation of that is that the old man ultimately didn't think his son would win the whole thing, he was ready to break his own heart and see Gi-hun fail. This may also explain why he himself stalled the licking technique and was yes, using saliva to cut his own, but being slow. He was perhaps willing even to swap the candies if need be (I know, this is a stretch) but if you realise that if the rules dont' stop something then anything goes, then you'd understand.
What really confused me about the honey candy game was that the guards were so blatantly mispositioned to see some while watching others like hawks, it was perfect for cheaters, as we saw with the 'lighter' chick who would have had it confiscated and been killed/eliminated for ruining the 'entering the game as equals' concept etc. Even weirder was the Deuk-su was in sight of the cameras even if the guards weren't watching him. Surely one of the guards at least spotted what Deuk-su was doing. The only explanation I can think of is that the square guard who was involved with the organ harvesting saw it and didn't snitch because he planned on the doctor allying Deuk-su for a near-guaranteed win of the tug of war later on. That is the only explanation I could think of there. There is no way that the lighter being involved in the game matched the front man's 'equality' mantra.
