In general, each user will have several open Lightning channels and that should all be handled by the client you are running. Even with several open channels, while each channel may not be able to make a single large purchase, it is possible for you to make a large payment by sending money through multiple channels.
While there may be several large hubs, it certainly does not introduce that much centralization. Hubs can't change the amount of money that you have and can't dictate anything that you do. If a hub is misbehaving, you can simply stop using them and use someone else or just not use LN.
The problem I see with the "just not use LN" argument, is that once Lightning network is widespread and we have channels all over the world filling flocks with all these microtransactions, the overall on-chain fee will be higher than ever, at some point it will be non-viable for most people to transact on-chain. For people using LN, it wouldn't matter, as their transactions will eventually go into a block mixed with the rest of LN transactions (btw, who sets the fee for an "LN-tx filled block"?) but for people that want to transact on-chain, it will be extremely expensive, unless im missing something here.
PS: Im not saying "make blocks bigger as soon as they get filled" and such nonsense are a solution, im just pointing out at how widespread LN usage could lead to unusable on-chain transactions.