I wanna point out what I think is an important distinction when it comes to Leo’s self-sacrificial tendencies.
People tend to view self sacrifice as akin to suicidal tendencies, which while can be true, I don’t think fits Leo (or any of these characters). Leo has insecurities, yes, but he doesn’t view his life as less valuable. I don’t think he believes his brothers think that, either, even if he doesn’t think they trust him, worries they may not like him sometimes. Leo knows they love him.
Leo understands the strategy of self sacrifice. The only situations he’s willing to throw his life away are when it will save his brothers (and, perhaps ironically, when he believes he’s at fault for the danger they’re facing). He offers himself up in the maze of death, to Piebald, and to stop the Krang.
This is not because he thinks he’s less than, it’s because losing one of his brothers is his worst fear. He was devastated by Karai’s death, CJ throwing his families mortality in his face is what gets him to learn a vital lesson.
Leo doesn’t want to die. It’s written in the despair paralyzing him in the prison dimension. It’s is his last resort because the idea of losing them is scarier than his own death (which also terrifies him). If it means saving them, he’ll do it every time.
Every single one of these characters would die if it meant saving each other. None of them want to live in a world where someone is lost—they’d rather it be them. Because the most important thing to them is each other.
It’s not that they view themselves as expendable. It’s that they value each other more than anything else in the world, even their own beating heart.
When the world is ending and there’s no other options, he even asks it if his brother, because there’s a chance they can save the world with the last of his power.