with the 1MB blocks currently all full, i seriously doubt thats true.
what happens when a payment channel with 10,000TX needs to be settled on the blockchain?
My statement is wrong (read above). However, the answer to your question is: It needs 1 transaction on-chain (to close the channel).
30 million users making a transaction..each.. ONCHAIN to lock their funds into LN
then 1 transaction ONCHAIN filled with 30million-60million outputs to settle the balances with the destination while also returning the 'change' to the originator meaning atleast 2 outputs. destination and origin, for every input.
now do the maths