Not sure where you are getting this number from? Even if we say that bitcoin goes to $1 million, and you can open a Lightning channel in a transaction of a few hundred vbytes in size, then with a fee rate of 1 sat/vbyte you are looking at $2-3 to open a channel. Even if we go up an entire order of magnitude say it's going to cost you $30 to open a channel, if I then use that channel to make a few hundred transactions over a period of months, then it is overall it is still cheaper than had I made all the transactions individually.

You can always rebalance channels, and there are new developments such as channel factories and Eltoo which allow multi-user channels. With enough global adoption of bitcoin, there will be enough volume on the base layer simply from opening and closing Lightning channels (or some other layer two mechanism) to maintain the security of the network.

It may be that a further block size increase is needed in the future, but we are nowhere near that stage yet.