Rendering is a final stage of creating an animation, so you need to make a story, illustration and animations before you start rendering video.
Second, why you assume, that i assume, that he can't wright? I belive that he can wright a more developed story, if he took some time to it, but quality wise it still goin to be average at best. That's not what i meant at all, I'm talking about how long it will take him to make a video. Creating a more detailed plot and make an additional illustrations will took additional time to make a video. And coming up with a short but well-developed plot every couple of weeks, is quite difficult if you are not a professional writer.
'Bout your solution - second variant with the stories from the internet might occasionly happen like that one Amanda episode, but it looks like, that he mostly want to make his own stuff. And of course he never going to lurk on forums like this, in search of creative material for his content - If you don't pay money to creator for his work, he will don't give a damn.
And idea about bringing an author - if he's not hired anyone, than he might simply don't want it, or don't want to spend money on it. And btw, you need to find not just a writer, but a writer with experience and discipline. A wrighter who will constatly deliver new plots. Animations with huge plots are very rare (and huge, long animation not always equal a long plot), so lets look at RPGM and Ren'Py games. A lot of this projects have a descent or even good wrighters, but lot's of them lacks discipline - constantly fuck up all deadlines, runin out of ideas, abandoning projects halfway, etc.
So if you really need a good and reliable wrighter, you need to spend a good amount of money to pay him. And hiring such author will not guarantee, that you start gaining much more money from your works, so in the end it might turns out, that you will make less money for yourself, after wrighter gets his cut. So now it's you making assumption that hiring an author will be easy and cost almost nothing, but let's not forget - making animation full time is a work, and content creators like all of us, has to pay their bills so that there is still some money left to support their alcohol/drug addiction, or, well, for something else, like buying food.