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Common answer:
The "their kid" effect: why "my kid" is so.... ?
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Serious answer:
The support he gets at the early game is crucial. Especially when against hard match-ups.
Yes, I'm pointing the finger at your jungler. If you gets a jungler who plays smart by strategy rather than mechanics, your "scale" champion will get good result. Either mid lane or top lane, if your jungler has wide knowledge about champions strength and match-ups he can nurture the lane with better scale and better roaming, making it "pivotal change" to snowball the game.
In reality, many junglers play by instinct, or should I say randomly. And they didn't even think about the strat at the pick/ban phase, and such. That's also the reason why you see random results for a "scale" champion.
When I said about "scale" champions, people may think of Nasus, or Ryze. They are correct, however they should know there are other scale champions as well, like Yasuo and RoA-based champions. If your jungler (and your team, generally speaking) is aware of that and can adapt the play (like, taking 1/2 HP of the opponent mid so that he doesn't dare to farm in next 3 minutes), your Yasuo can carry.
Even when Yasuo were killed a few times, if he has time to farm for free he can comeback. Be patient with his weak early game and he'll pay back your team later. Don't be a "random" jungler and camp lanes where they don't actually need it (like Tahm Kench, Malphite, Maokai, ... although looks like their lane is pushed).
The only diplomat is when you are the jungler and both your mid and top are "scale" champs, what to do? Let's say it's Yasuo and Ryze. Okay the answer is based mostly on the match-ups, and partly on the opponent jungler.
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If your Yasuo is against the Varus, Ziggs, or Ezreal; he'll do fine generally without the interfere from junglers. You may camp the Ryze lane then.
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If your Yasuo is against the Annie, Swain or Kayle; he'll need good skills to get early advantage. But chances are he'll be poked early and start losing in CS then some LV6 burst or LV7 all-in and he'll starts falling. That's why you (jungler) should camp around his lane, babysit the Yasuo and take some HP of the lane opponent. A success gank is a kill or some SS+HP is forced, but in the case of scale champs some HP is enough, he'll scare of the opponent and start lane dominance. Now you have more time to farm or gank other lanes or trying perform some nice mechanics, whatever...
That's it.
P.S: Don't pick Nunu. Also bear in mind that some "lv6 gank" junglers actually can gank pre-6: Warwick, Sejuani, Malphite, Yi, Kayle, ...