DNC will be challenged in court for illegitimately changing candidates before the General Election. In a Trump backed court. And it will be a swift trial unlike the ones aimed at him.
How can we expect them to defend democracy if they can't even win that fight? It's a non-issue, the precedent is clear that political parties can choose their candidate at the convention. 'Presumptive nominee' is not an official position, it's just a description of a situation. Why should we fear frivolous legal challenges?