I just don't think he's all that good a politician. He's very good at coming across as serious, and that should in theory work well against Johnson's bluster, but it just doesn't chime with what the British public wants from it's elected officials. He's totally lacking in charisma and personality, whereas Johnson has it in droves.
As for clear terms, I agree. Unfortunately they've lost all sense of reason and are doubling-down on focus groups and Blairite thinking about how to win over undecideds and lite-Tory voters, at the expense of those that have, and will continue to vote Labour. You can't out-Tory a Tory.
Unfortunately there's a complete dearth of talent in the ranks; both on the right and the left of the party. Even if we did change it up, I'm not sure where they'd turn.