Yeah that’s my understanding with lighting because as some people have argued here Muun isn’t a true lighting wallet.
It basically stores everything on chain and takes temporary custody of your sats to send via lighting.
This is why it does that seemingly cool thing where you can choose to send your Bitcoin over L1 on chain or L2 on lighting.
You might also notice that the lighting fees may be on the higher side vs using a conventional lighting node/wallet and I think it’s because of the onchain fees. This I am really just speculating on and someone please correct me if wrong.
The trade off with Muun being stupid simple is you don’t get access to utxo management.
Funny enough I use Muun to convert onchain to lighting to send to my self custody node.