Yes, that is a possible threat, that large hubs can go down like Wallet of Satoshi or Bitfinex and it would lock up a bunch of capital. But I would argue that the network will respond, in the beginning, payments will fail, but people can quickly bring online new channels, close channels to those hubs if they feel they won't come back.

While channels that are large and up, can advertise for more liquidity and offer a larger yield to get more capacity coming online and pointing to them

In fact, I would like to see this go down in practice so we can see how wrong LN really is and what we can learn from it