Kog'maw standing still outduels an assassin.

Okay, sure, all the reasons you just put forth in this comment are valid as to how Talon can lose to Kog'Maw one-on-one, but that's not what you said in the comment I replied to. The fact that your initial comment tried to defend the possibility of Kog'Maw, the least independent marksman in the game, outdueling an assassin, using no information from any particular match and without bringing up the assassin potentially messing up, on the argument that he is meant to kill anyone who doesn't reach him within an indeterminate amount of time, does not really demonstrate that same balanced viewpoint you are trying to put forth now.

For sure, if the assassin doesn't play right, they will die, but if Kog'Maw doesn't play right, e.g. if he mispositions and gets caught out by the assassin alone, he should die as well. It is also worth mentioning that the criterion here for Talon "playing right" is successfully approaching Kog'Maw and landing his entire combo (which is admittedly easier to do on a stationary target), whereas the criterion for Kog'Maw to succeed here is, by your judgment, to "stand still and hope they die before they reach you". Because of this, I do think there's a bit of unfair judgment going on here, as the argument as it has been framed gives Kog little room to fail, and puts the onus on the assassin to not only land their entire combo in order to kill him, but also to survive a stream of damage they should naturally be more able to stop with significantly more burst damage. By all rights, it is the assassin here who should have relatively less room to fail against Kog'Maw, because Kog is one of the least mobile, most defenseless targets in the game, with his only assets being range (which assassins can bypass via mobility) and DPS. Even if the assassin is somewhat behind, they should still have enough natural leeway to be able to deal with him, just as Kog is naturally well-equipped to deal with tanky melee opponents.

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Yes, they are, and yes, they still can...if they play right. For instance, Talon ulting in and getting the drop on Kog before he even knows he's in danger. But if Talon disrespects that damage, he's going to die. As I said, assassins are just as squishy.

Being as OP has given no context or proof of how this happened, Talon misplaying how to go about assassinating is just as likely of happening.

An extra 700 health and 30 armor are hardly going to mean anything vs a Talon with two lethality items and Duskblade. However, in this situation, Talon is dreadfully behind. Kog'Maw had 11200 worth of items. Talon? Only 8100. That's 3 full items against 2 and a 3rd with a difference of 3100 gold. So given the lack of evidence that Talon did his job correctly, and the evidence that Kog'Maw was very far ahead of Talon, it's quite obvious why Talon died.

Yes that is a possibility but is it as plausible as you say it is? Nope 9 out of 10 time assassins win, the few times they don't it's because of various factors that work against them.

That said. Assassin are a nature counter to immobile ADC's