Ryze is pretty good lategame too - definitely better than taliyah. But fnc played like it was all on twitch. Like you said - they put all eggs in 1 basket and made 1 bad play that lost them the game. Just like pob knew he was badly outscaled, but exploited reckless aggression and baited him into death. Honestly even if they'd traded 1 for 1, it would have been gg with imt winning. That pob lived was just icing on the cake. With supers rushing in top, all fnc had to do was either 5 man bot or 4-1 bot with solo person mid. You can even bait enemy into killing the solo person mid if it gets you the 2nd inhib bot. Because losing 1 person (as long as it's not the adc) in exchange for 2 inhibs is worth that late into game. Either they buy enough time you get inhib plus escape rest of your team, or they die fast 1v3 mid and you get inhib plus a 4v2 doublekill bot - making it a 4v3 with 2 inhibs down.
And the other thing you can do with lee is just kick the adc away. Like if adc can only focus lee and twitch is blowing up the 4 others on imt while they peel lee off twitch and kite back to their adc, imt just loses. Sure lee's not really useful late game aside from the perfect insec, but jayce isn't any more useful for teamfights. And in their team comp, lee wasn't picked for the late game. He was there to get twitch fed early and give fnc a solid early/mid lead; which he did. I don't think another jungler could have pulled off the same level of lead that early into game - sej comes close, but I think 1 or 2 of those early ganks wouldn't have quite been as successful with her - either imt would have just survived or they would have traded kill bot instead. So yes, lee was bad late, but you also must consider what he did for them early/mid and how much of that advantage they wouldn't have had in exchange for getting a better late game alternative jungler. I guess we will find out in the repeat match next week.