Like others have said, it's not necessarily about small channels working hard and big channels not doing so, but instead it's about how they work. Smaller channels, by and large, will be run by a smaller group of people, most of the time a single person and sometimes couples or whatnot. When you're in this kind of environment you have to become a jack of all trades and do your best at every step along the film making process, from conception to Youtube upload and SEO optimazation.
Again, generally, larger channels will have more people working on them, so the personality of the channel doesn't necessarily do every bit of work including editing, sound effects and foley, or any other step. Does this mean that the larger channel peeps don't work as hard? Not necessarily. Although each person probably has a more specialized role, the onus is also on that person to create stellar content in the role that they are providing. There is a lot more pressure, and in many cases there is a standard of content that has to be lived up to that is very high.
Anyways, I think small Youtubers might work harder in many ways, or like Xingcat said, they have to "hustle". But at the same time, the larger channels have pressures, expectations, and deadlines that I can imagine are tough when you have to force your creative process along at an accelerated pace. In conclusion, there's no way to really tell who works harder, all you can do is work your hardest, work your smartest, and eventually it should be noticed.