2) Why would Obi Wan leave Skywalker there like that to burn to death? Seems like the Jedi way would be to end his suffering right then. Plus obviously it is sloppy to assume someone is defeated.
Because anakin would've died. The emperor didn't tell anakin the story about his former master being able to keep people alive with the force for anakin's benefit. The emperor hoped to have that power.
He used that power to keep anakin alive.