It's not accurate to think of Ln as a separate token moving on top of BTC
 It's better to think of it as a network that claims ownership of sats inside BTC multi-sig contracts
 There's no way to claim ownership of a sat that doesn't exist.
ie you cant create supply from nothing 

The best anyone can do claim the sats in the channel (multisig contract) from their counterparty and hope they can get away with it. 

 Assuming people will only use L2 because it's cheaper, they will never settle the transaction on Bitcoin network, do you think it's impossible to cheat ? 

 its only possible to try and steal your channel counterparty's sats.
and you're penalized if you try and they prove you are trying to cheat.

it's not something we hear a lot about... so I'm feeling like it's not a big problem?