I'd take most of those big sub numbers with a grain of salt. Subbing is so easy to do, and very subject to rigging. Actually watching the videos is another matter. That's where content still matters. And luckily, that's what pays: (monetized) views, not subs. (Although you can work out marketing deals based on your subs, you won't be able to do that forever if you don't come through with the views).
I celebrate sub milestones like anyone else, but so many of those "big" YouTubers get a lot of attention and have big sub counts, but in reality many of them are not bringing in nearly the views that they could be, given the number of subs they have. Take Shane Dawson--no doubt he's a successful YouTuber, right? His main channel has over 6 million subs, putting it in the top 100 of all YouTube channels for subs. And he has over a BILLION views, so he must be doing something right, right?
But average current daily views tell a different story. His main channel currently averages around 250k views per day. Most people would love to have a quarter million views per day but given how many subs he has, and his historical views, that's actually a pretty low daily view count. I know there are several YTtalk members getting much higher daily views than Shane (including my channel), with only a fraction of his subs. Why? Because people are actually watching the videos, which leads to them getting suggested more by the YT algorithm, which leads to more views.
I'm not just picking on Shane, there are lots of household name YouTubers who are very good at grabbing the headlines and getting subs, but aren't coming through with the daily views. Look at the next panel coming to Vidcon--I guarantee there are guests who were invited as "celebrities" based on their sub counts, maybe even a few with some good views numbers behind them, but as for daily view count, they aren't as high as a lot of other channels. Not everything they release is going to get viewed by millions, even subs and fame aren't guarantees--the content has to be there.
So content does matter, although let's face it, "'quality" is a very subjective matter of opinion--we've all seen popular channels that we'd never want to watch voluntarily again!