Would this model work?

Creators themselves PAY to upload/host something. Their in-video ads are what allows monetization.

No adds at all from youtube. Uploading COSTS money, maybe a few dollars.

Creators make their money solely from sponsors or selling/advertising something themselves.

That model already exists, it is called the internet. There you pay for hosting and advertisements and everything, and you also get all the revenue.

It isn't very popular since the internet doesn't advertise your content for you, youtube do that so its much easier for content creators to get big on youtube. Also it is free to upload on youtube, so small creators start there, small creators later grow to big creators and stay on youtube.

serving video costs money not just uploading. so there has to be fixed and variable costs - but if that is accounted for then it could work but we are putting all the risk on the creator.