You don't have to say everything is going to be okay. You just can't tell him "you suck."
It's not a binary state between insulting and coddling -- there's a third option which is to simply not engage in conversation about his performance. There's also the option to say something like "Dude -- Renekton is far enough ahead that he'll eat you alive if you go close. Just farm under tower as best you can." Does that imply that maybe he fed Renekton a bit too much? Sure. Does it do so in a relatively non-offensive manner and offer a suggestion for what he can do now? Also yes.
So you have options if you don't want to pamper him. Insulting him just isn't one -- or, rather, it IS an option, but it comes with consequences in the form of account punishment.
There also is something to account for consistent bad ranked play -- losing MMR. You'll quickly end up among players better suited to your current skill level. But also remember that players have bad streaks: looking at yours, for example, I see at one point a while back you had an 17-game streak with only 3 wins it in. Do you feel that would merit the "no ranked" punishment? I'd argue it shouldn't -- you're still the same player, and you're just having a bad run of it. It happens.