To me trusted third party is like, when someone else is holding my funds and if that party goes under, I lost all funds.

With opening lightning channel on the other hand, I'm not giving the custody to the other side in the same sense. If the other side escapes, my funds can always be retrieved, minus the current onchain fee.

That's how I look at third party. On lightning I don't necessarily trust the other side and only trust there is, is in the lightning protocol.