The "centralization" that most people talk about is really about limiting who can effectively (and profitably) participate.
If we're talking about the blocksize debate, the idea is that larger block sizes require faster internet connections to remain competitive and at a certain point this might make it infeasible for any but a few large companies to be profitable mining blocks. If this is true, because bitcoin is essentially controlled by miners, this could lead to a different group of people controlling bitcoin than do now (ie perhaps a group we don't want controlling bitcoin).
If we're talking about the lightning network, the idea is that larger hubs would have the advantage over smaller hubs because they'd be more likely to have a route to whoever you want to pay and those routes are likely to have fewer hops. The thing is, if this is true it doesn't really affect Bitcoin. Even if the result is that everyone is connected to one single hub, that hub has 0 power to influence miners. If that megahub ends up being a bad actor, someone can easily switch to another hub. There might be some privacy issues with a megahub, and they could censor transactions, and that kind of thing, but it wouldn't be able to steal your bitcoins nor would it be able to hijack the consensus rules of bitcoin for its own gain.
My opinion is that the advantage of having fewer network hops isn't really much of an advantage. Its much more likely that many medium-sized hubs will be created, not the least reason being that people are going to want to connect to multiple different hubs in the case that one of them goes down for some reason.
So tl;dr, the LN doesn't really have a major centralization pressure, and even if it did, the centralization wouldn't cause any major problems.