Why be wary of someone who could quite successfully split the (D) vote by running third party? After all, that’s what they’re hoping Trump will do.
I respectfully disagree with both assessments of Bernie. Bernie's purpose is not to win the election. And the Dims have shown they can effectively use him without splitting the party.
IMHO Bernie's purpose is to move the political discussion even further to the left to normalize socialism even more than it already is for whatever Dim they hope wins. Brandon is in many ways further left than Obama or Clinton or any prior WH occupant. But the Dim voters feel like Brandon is a "moderate" contrasted with Bernie's uber socialist talk and all the Bernie-likes that try to out-Bernie Bernie (i.e. A Occasional Cortex, or Fauxahontis).
So if a Dim wins 2024 he'll be even further left than Brandon in large part because he can say he's not as extreme left as Bernie.