No you're right, this particular behavior doesn't help to preserve their monopoly. It's evidence that they already have one.
Companies who have to survive in a competitive marketplace don't typically go around driving away customers en masse. This is like something from 1990's Microsoft.
Having a monopoly isn't illegal. Using monopoly powers in certain ways is, and this isn't one of those ways.
And yes, companies who have to survive in a competitive marketplace drive away non-paying customers all the time. Because they're not paying, and so the slight chance of turning them into paying customers, or benefiting existing paying customers, is worth the loss.
Well, strictly speaking, this is a legitimate dictionary definition that doesn't involve money:
> a person of a specified kind with whom one has to deal
[edit] Youtube has 3 kinds of customers (or users, if you wish): publishers, viewers and advertisers. It makes sense to separate them like that, but not based on a "pays/ does not pay" criterion. If PewDiePie is a customer, then most definitely Blender Foundation is a customer too.
If money is the criterion of being a customer then they are one by driving traffic to other monetized videos, via recommended feed, or via follow up searches, that would otherwise not happen.
Anyone having a YT channel will tell that ‘suggested video’ is a dominant traffic source so it’s not an edge case.
In sum, YT was already making money thanks to Blender videos.
Companies who have to survive in a competitive marketplace don't typically go around driving away customers en masse. This is like something from 1990's Microsoft.