in this specific case, imagine if we had thousands of mini-youtubes, each with their own curational quirks. no single mini-youtube could unduly influence the whole zeitgeist. most (all?) will be flawed in their curatorial duties, but none could move public opinion in any meaningful way. viewers could also jump from one to another and be exposed to many different editorial perspectives, even without necessarily being cognizant of that. however, if every mini-youtube were relegated to being a single person each (i.e., no centralization), then we'd lose the benefits of aggregation and curation.
the problem of course, is that we societally accept size and growth as good things, and i'm arguing that they're only good to a certain point (and see your argument as saying all centralization is bad), and that we need to change incentives as a function of size/centralization, so that we get right-sized organizations, rather than unaccountable behemoths. our current incentives make right-sizing an unstable equilibrium point on that curve, which is why it doesn't happen.
centralization is merely a necessary but not sufficient ingredient for dystopianism. you also need a ratcheting consolidation of power, especially money (provided by advertisers in this case) and attention/influence (provided by viewers). centralization is simply one of those (key) ratchets that can be leveraged to further consolidate power for the benefit of directors and executives.
relatedly, the american constitution is an experiment in crafting a centralized system with checks and balances stable enough to withstand assaults of power consolidation. the jury is still out, but it's looking somewhat bleak at the moment, given a runaway executive branch fueled by an unhinged fed/central bank. we seem to be stomping on the gas pedal even as the brick wall looms ahead.
in any case, i've long been an advocate of right-sizing organizations of all sorts, especially governments and companies. we've concretely learned over the past many decades that the negatives of large (and small, but those tend to self-regulate away) entities eventually far outweigh the benefits, and are better substituted by a more diverse and specialized collection of medium-sized ones.