The Lightning Network literally exchanges Bitcoin transactions that are withheld from being broadcasted on-chain until channel closure. Bitcoins exchanged via the Lightning Network are just Bitcoins. Saying they are a different kind of "IOU" or token is a lie often employed by alt-coiners trying to push a "Layer 1-only"-Bitcoin fork (e.g. BSV).
The security in the Lightning Network doesn't come from settling on-chain after a transaction happened but from signing over all your money in a Lightning Network channel to the other party should somebody catch you cheating.
The real lie is saying that LN transactions are "just Bitcoins".
They are unconfirmed transactions and there are many ways of losing your funds compared to confirmed ones. Such as having your harddrive corrupted and your node trying to propagate an old state.
Unconfirmed Bitcoin transactions are still Bitcoin transactions, with the advantage that on the Lightning Network you have a built-in protection against doublespends in contrast to accepting 0-conf tx.
You are correct that funds in a Lightning Network wallet are at higher risks than those in a cold wallet, but this applies to all "hot" crypto wallets. Most LN wallets supports "Static Channel Backups" which you only create and store once after setting up a channel. In case your phone goes up in flames, you can use it to safely close your channels and receive your balance.
